Framing Preparation for Railing Posts

Before any railing posts go in, the framing or slab they mount to needs to be ready for them: decks, balconies, landings, lofts, stair openings and concrete slabs, inside and outside. Standard framing is built to carry people and furniture, not the sideways push and pull on a guard post. This page covers the framing prep that is standard across the industry for fascia (side) mount and surface mount posts, on wood and on concrete. It applies to any brand of railing post, with extra notes for cable railing. Any general contractor can do this prep.

Why Framing Prep Matters

  • Guards must resist a 200 lb load at the top rail, in any direction. Building codes require it, and that load is carried by the post base and the framing behind it.
  • Cable railing adds high cable tension on end and corner posts, pulling on them all the time, not just when someone leans on the rail.
  • Standard framing is not designed for this. A single rim joist nailed to the joist ends, over single 2x joists, can twist or pull away under post loads.
  • Blocking, doubled members and proper fasteners are standard practice. The American Wood Council's DCA 6 prescriptive deck construction guide shows the same approach.
  • Plan for rail height after finishes. Rail height is measured from the finished surface, so tile or thicker decking reduces it. Aim for 42" or more after all finishes are in. A little extra height gives you margin.

Mounting Options at a Glance (V4)

One post, several ways to mount it. Pick the mount that fits the job; every option uses the same 2" x 2" post.

Mount Best for Hardware Status
Fascia flange (5x7, corners, concrete end) Outdoor decks, balconies, commercial work, concrete slab edges 1/2" 316 through-bolts + backing strip (wood), or 1/2" 316 rod in adhesive anchors (concrete) Main engineered mount
Square surface flange 4" x 4" Decks, slabs, patios, balconies, stairs 3/8" x 8" 316 lags (wood), 1/2" anchors (concrete) Main engineered mount
Slim surface flange + slim L corner Interior balconies and openings where the post must sit close to the edge 3/8" x 8" 316 lags Premium option, load test pending
Direct mount (screws through the post) Stairs, stringers, lofts and tight spots where a flange does not fit 2 or more Simpson SDWS Timber SS (316) screws, field drilled, into 3" of solid wood Light duty. Not part of the engineered system; confirm with your installer or engineer

Fascia Mount: Wood Framing

  • Do not use lag screws alone. A typical build is a 1-1/2" fascia board over a 1-1/2" rim joist. That is not enough wood for lag screws to hold a guard post.
  • Through-bolt every post. Use 1/2" stainless steel (316) bolts through the post flange, the fascia board, the rim joist and the blocking. On the back, use a 1-1/2" x 6" x 1/4" stainless steel (316) backing strip and nuts. One backing strip fits every post: it runs flat across both bolts on middle and end posts, and upright behind the single bolt on each face of a corner.
  • Set the height, then lock it. Drill the framing on the rim center where possible, bolt through the flange slots, set the flange top at the top of the rim, tighten the bolts, then drive the two lock screws. See Slotted Fascia Flange.
  • Lay out posts between joists. If a post lands on a joist, center it on the joist so the two bolts straddle it, and use a separate washer on each bolt. Never mix a lag screw into the joist end with a through-bolt on the same post.
  • Add solid blocking behind the rim at every post. Use full joist-depth lumber, fitted tight between the joists on each side and fastened to both joists. The bolts pass through the blocking. The blocking stops the rim from rolling off the joist ends, which is the real weak point.
  • A doubled rim joist is also acceptable, but blocking at each post is still recommended.
  • Add a tension hold-down at end posts, corner posts, and weak or older rims. A hold-down such as the Simpson Strong-Tie DTT2Z ties the blocking back to the joist.
  • Composite or PVC fascia: put a solid spacer behind the post flange so the bolts clamp onto the framing, not onto the trim board.
  • Plan for access behind the rim. The nuts go on from behind. If the underside will be closed in with a finished ceiling, install the blocking and bolts before the ceiling goes up.

Fascia Mount: Concrete Slab Edge

  • Use adhesive anchors, for example Hilti HIT-HY 200 or HIT-RE 500 V3, with 1/2" stainless steel (316) threaded rod.
  • Drill with a 9/16" bit to a minimum embedment of 4-1/2" into the concrete.
  • Keep anchors away from the slab edges: at least 4" from the top edge of the slab (6" preferred) and at least 4" from the bottom edge. In practice this means a slab about 8" thick or more. For a thinner slab, use a surface mount or a custom solution.
  • Concrete strength matters. Plan on structural concrete of at least 4,000 psi. Older, cracked or unknown slab edges should be checked by an engineer, or use a surface mount set back from the edge.
  • A taller flange is stronger. The farther the bottom of the flange reaches below the anchors, the more leverage the flange has against the slab face, and the less pull on each anchor.
  • Outside corners: anchors drilled from the two faces of a corner can run into each other inside the slab. See Corner Posts below.
  • Clean every hole: blow out, brush, and blow out again before injecting the adhesive.
  • Let the adhesive fully cure for the time the adhesive maker lists before loading the anchor.
  • Tighten the nuts to about 30 ft-lb, or to the adhesive maker's installation torque.

Surface Mount: Wood Framing

These notes are for the 4" square surface flange (8 holes, 1-1/2" apart). See Surface Flanges below for the drawings.

  • Three boards of solid wood under every post (4-1/2"). The front lags go in the center of board 1 and the back lags in the center of board 3. No lag ever sits on the seam between two boards.
  • Outside edge (deck or balcony rim along the rail): a structural 2x fascia (treated, Douglas fir or cedar, full 1-1/2", screwed to the rim) is board 1 and the rim is board 2. Add one 2x block behind the rim, fitted tight between the joists at each post, as board 3. The post face ends up about 1-1/4" from the fascia face.
  • Composite, PVC or 1x trim fascia does not count. The rim becomes board 1: add two 2x blocks behind it. The post moves back 1-1/2".
  • Interior edge (loft, balcony or stair opening): the doubled header is boards 1 and 2. Add a third 2x behind it at each post, plus blocking to the next joist. See Interior Balconies below.
  • Side edges (rail parallel to the joists): double the end joist and add a third board or blocking so there are 4-1/2" of solid wood at each post.
  • Corners: the same square flange. Run the added board 3 on both edges right into the corner so all four corner holes land in solid wood.
  • Fasteners: 3/8" x 8" stainless steel (316) lag screws in the 4 corner holes, pre-drilled. If a corner hits a knot, a split or a joint, use the middle hole in the same row. Always two lags in board 1 and two in board 3, never fewer than four.
  • Decking under the flange: wood decking can stay. Composite or PVC decking crushes: cut it out under the flange and install a solid treated-wood pad flush with the deck surface.

Interior Balconies and Floor Openings

A loft, a balcony over a living room, or a stairwell opening is framed differently from an outdoor deck.

  • The edge is usually a doubled header, not a solid beam. Older houses use doubled 2x10 or 2x12 (3" wide). Newer houses often use I-joists with a doubled LVL or a rim board at the opening.
  • I-joists need solid blocking. You cannot lag into the thin top flange of an I-joist. Add solid blocking or filler blocks at every post.
  • The edge member runs along the rail, like a rim. Add blocking behind it so both post fasteners land in solid wood.
  • There is usually no access from below. With a finished ceiling underneath, use lag screws or structural screws into blocking, and install the blocking before the drywall goes up. On a finished house, plan to open the ceiling or the floor at each post.

Interior Balcony Edge: Layers and the Slim Surface Flange (Premium Option)

This is a typical interior balcony or stair-opening edge, with every layer shown. The edge member is a doubled 2x10 running along the rail, with drywall on its face and on the ceiling below, and subfloor and finish floor on top.

  • Measure from the finished wall face. Behind 3/4" of drywall and trim, the first board of the doubled 2x10 is centered 1-1/2" in, and the second board 3" in.
  • Center each lag in one board, never on the seam between the two boards. A lag on the seam only bites half its threads and wedges the boards apart.
  • Standard: the 4" square flange with a third board added behind the header (see Surface Flanges). Premium option, shown here: the slim surface flange, 3-3/4" along the rail x 2-1/2" across, with four 3/8" holes, pending a load test. The two rows are 1-1/2" apart, so one row lands in the center of each board. The post face ends up about 1-1/4" from the finished wall face.
  • Fasteners: 3/8" x 8" stainless steel (316) lag screws, pre-drilled, through the finish floor and subfloor into the header.
  • Blocking at every post: a header running along the rail can roll like a deck rim. Add double 2x blocking between the header and the next joist at each post, fastened to both, before the ceiling goes up.

Interactive model: drag to rotate, pinch or use the zoom buttons, two-finger or right-drag to pan. Orange = lags in the first board, blue = lags in the second board.

Surface Mount: Concrete

For slabs, patios, balconies and concrete stairs, with the 4" square surface flange.

  • Standard: two 1/2" anchors in the middle holes, 6" deep, 3" from the slab edge (post face 2" from the edge). Use the 7/8" slim washer and 1/2" jam nut from the kit. At corners, use the two inner middle holes so both anchors stay 3" from every edge. About 2.2x by the numbers; engineer check or load test to confirm.
  • Heavy-duty: four 3/8" anchors in the corner holes, with the front anchors at least 4" from the slab edge (post face about 4-1/2"). The most margin, both leaning out and pushing in.
  • Slab thickness: at least 6" for 3/8" anchors, at least 8" for 1/2" anchors 6" deep.
  • Scan before drilling. Have the slab scanned (GPR) and never cut rebar. On post-tensioned slabs, common on condos and balconies, do not drill until the tendons are located. Cutting a tendon is dangerous and very costly. If rebar blocks a corner hole, use the middle hole in the same row.
  • Adhesive anchors such as Hilti HIT-HY 200 or HIT-RE 500 V3 with stainless steel (316) threaded rod. Drill straight, never angled. Clean every hole (blow out, brush, blow out again) and respect the adhesive maker's cure times.
  • Expansion (wedge) anchors: 316 stainless, rated for cracked concrete (for example Hilti KB-TZ2 or Simpson Strong-Bolt 2), at the maker's edge distances. Drill the hole deeper so the stud does not stick up past the nut after tightening: wedge anchors rise when torqued.
  • Stick-up: no more than about 1/8" above the nut, so the 1-1/8" base cover sits flat.
  • Tile or pavers on top: use a longer rod so the full embedment is in the concrete. Set the flange on a non-shrink grout pad, or cut the tile out and bear directly on the concrete.
  • Leveling: stainless steel shims or a grout pad, never plastic shims under load.
  • Post outside the slab entirely: use the fascia flange on the slab edge instead (see below).

For more on base plates and anchoring methods, see How to Anchor Railing Posts.

Surface Flanges: Square Standard and Slim Option (V4)

  • Square surface flange (standard): 4" x 4" x 3/8", 8 holes on a 1-1/2" pitch (hole centers 1/2" from the edges). Corner holes 7/16" for 3/8" lags or anchors, middle holes 9/16" for 1/2" concrete anchors. Same four M10 screws hold the post. Works on wood, concrete, corners and odd framing.
  • Base cover: 4.13" square outside, 1-1/8" tall, 1.2 mm wall, 2.04" post opening. Clears a standard 1/2" nut, about 1/8" of stud stick-up and about 1/8" of shims.
  • Hole guide: standard = the 4 corners, two in board 1 and two in board 3. Backup = the middle hole in the same row. The side middle holes land in board 2 and are extras only. Never fewer than four fasteners.
  • Slim surface flange (premium option, load test pending): 3-3/4" x 2-1/2" for wood with two boards (doubled header, or structural 2x fascia plus rim). The post sits 3/4" closer to the edge. Corners use the L-shaped slim corner flange so the posts line up. Not for concrete.
  • Target margin: about 2.5 times the 200 lb guard load (what the wood or concrete holds divided by the pull).

Base Covers (V4)

One cover for each surface flange: square, slim and slim L corner. Same rules as the existing cover: 1.2 mm wall, about 0.5 mm gap per side over the flange, 2.04" post opening, now 1-1/8" tall.

Base covers V4: square, slim and slim L corner

Surface Mount: Every Condition in One Layout

The same layout as the fascia models (deck, balcony, landing or floor edge against a house wall): middle posts, an end post at the house wall, an open end post, two outside corners and an inside corner. Use the Square flange / Slim flange buttons to switch between the standard 4" square flange and the slim premium option.

  • Wood, square flange: structural 2x fascia (board 1) + rim (board 2) + one added board 3 (yellow) at each post, run into the corners. Four 3/8" x 8" lags, two in board 1 and two in board 3. Post face 1-1/4" from the fascia face.
  • Wood, slim flange: fascia + rim only for the lags (one row per board); blocking behind the rim stops it from rolling. Corners use the L-shaped slim corner flange. Post face 1/2" from the fascia face.
  • Concrete, square flange: two 1/2" anchors in the middle holes, 6" deep, 3" from the slab edge; post face 2" from the edge. At corners the two inner middle holes are used so both anchors stay 3" from every edge.
  • Concrete, slim flange: two 1/2" anchors on the center line, 6" deep, 3" from the edge; the post sits in the same place as with the square flange (face 2" from the edge). The narrower plate shortens the lever: about 1.3x by the numbers, load test required. On concrete the slim flange gains no position; see the comparison below.

Wood framing, surface mount

Concrete slab, surface mount

Interactive models: drag to rotate, pinch or use the zoom buttons, two-finger or right-drag to pan. Wood: orange = lags in board 1, blue = lags in the back board. Concrete: orange = the two 1/2" anchors. White = unused holes.

Concrete: square vs slim at the same post position

Concrete surface mount, square vs slim flange, three options

Square flange: inside and outside, corners

Square 4 inch surface flange, inside and outside framing and corners

Slim flange and slim L corner (premium option)

Slim surface flange and L corner flange

Concrete options compared

Concrete surface flange options compared

Plate size study

Square surface flange plate size study

Fascia Flanges: Middle, End and Corner Posts

On wood, three flanges cover a whole deck: the 5" x 7" flange, the outside corner flange and the inside corner flange, all with 1/2" bolts and the same backing strip. Concrete uses the 5" x 7" flange and an end flange. The two models below show every condition on one deck, in wood and in concrete, with the bolts at the top of the slot (at concrete outside corners, the second face uses the bottom of the slot). Every fascia flange is slotted.

  • Middle posts: a 5" wide x 7" tall flange with the post centered. Two 1/2" bolts side by side, 3-1/2" apart, in vertical slots with a lock screw below each one. See Slotted Fascia Flange below. The post screws on with 4 x M10 (see Post Attachment).
  • End posts on wood: the same 5" x 7" flange as the middle posts. It can sit about 2" from a house wall, keeping the gap under 4".
  • End posts on concrete: an end flange with the post at one end and both anchors beyond it, the same flange as the concrete corner. Slotted like every other fascia flange. It keeps the anchors away from the end of the slab and still lets the post sit about 2" from a house wall.
  • Outside corners: on wood, one post with a one-piece corner flange. On concrete, two posts with the end flange on each face. See Corner Posts below.
  • Inside corners: on wood, one post with a one-piece inside corner flange and one 1/2" bolt per face. On concrete, two posts, one on each face, each on the standard 5" x 7" flange, set close enough that the gap stays under 4". The anchors from the two faces point away from each other, so they never meet.
  • Concrete: 1/2" stainless steel (316) threaded rod in adhesive anchors, 4-1/2" embedment. See the concrete notes above.
  • Wood: 1/2" stainless steel (316) through-bolts through the fascia, the rim and solid blocking, with the 1-1/2" x 6" x 1/4" stainless backing strip and nuts on the back. One bolt size and one backing strip for every post.

Slotted Fascia Flange (V4)

Every fascia flange now has vertical bolt slots instead of round holes: the 5" x 7" flange, both wood corner flanges and the concrete end flange. The installer drills the framing where the wood is best (on the rim center, clear of nails, knots or old bolts), and the flange slides to the right height.

  • Flange: 5" wide x 7" tall x 10 mm, post centered. The flange top sits at the top of the rim. 7" is the tallest flange that still fits fully on a 2x8 rim (7-1/4").
  • Edges: 1 mm x 45° chamfer around the front face of every fascia flange (the face you see). All other edges on every plate are broken 0.5 mm max, a drawing note only (not modeled).
  • Bolt slots (2): 9/16" wide x 1-9/16" long (1" of travel), 3-1/2" apart. The bolt can sit from 3" to 4" below the flange top; the middle of the slot is at mid-height (3-1/2").
  • Lock holes (2): 17/64" round, in line with the slots, 1" above the flange bottom, for a #14 316 stainless wood screw about 2-1/2" long (a concrete screw on concrete). Set the height, tighten the bolts, then drive the two lock screws. They stop the flange from sliding down if the bolts loosen as the wood dries. They do not replace tight bolts.
  • Why 1" of travel: anywhere in the slot, the pull on each bolt is no higher than with the old fixed holes (about 1,530 lb worst case at 200 lb on a 42" rail). A longer slot lets the bolt get too close to one edge of the flange, and the pull rises fast: about 1,880 lb at 2" of travel, 2,500 lb at 3".
  • 2x8 rim: the bolts land right on the rim center. 2x10 and 2x12: the rim center is below the slot, so the bolts sit at the bottom of the slot, with plenty of wood above and below.
  • Concrete: anchors 4" below the slab top; the bolt sits at the top of the slot and the flange top ends up 1" below the slab surface.
  • Corner flanges: the same slot and lock hole on each leg.
  • Concrete end flange: the same two slots and lock holes. At a concrete outside corner, the anchors on the first face sit at the top of the slot and the anchors on the second face 1" lower, at the bottom of the slot, so the rods from the two faces never meet. Both flanges and both posts stay at the same height.

Pick the rim, where the bolt sits in the slot and which way the rail is pushed. The panel shows the pull on each bolt. The wood is see-through so the bolts, backing strip and lock screws show.

Rough numbers for comparing bolt positions (the flange pivots on its top or bottom edge), not an engineer's stamp.

Post Attachment on Fascia Flanges (V4)

The post screws to every fascia flange with M10 x 30 stainless flat-head screws, countersunk from the back of the flange, into the four round bosses inside the post (3/4" bosses with a 1/4" core, on the same 1-1/4" square pattern the surface flange uses). One screw size for the whole post system. Screw the post onto the flange first, then bolt the flange to the framing.

  • 5x7 and concrete end flange: 4 x M10, 1-1/4" apart across the post, rows 1" below the flange top and 1" above the bottom (5" apart).
  • Outside and inside corner flanges: 8 x M10, 4 per face. Face 1 rows at 1" and 6", face 2 rows at 1-3/4" and 5-1/4", so the two screws that reach the shared corner boss pass at different heights and never meet.
  • Screw length: 30 mm = 10 mm flange + 20 mm into the post. That runs through the post wall, across the boss and out its far side; the tip just clears into the hollow.
  • Strength (rough): at 200 lb on a 42" rail the top screws see about 800 lb each (about 1,600 lb on the corner flanges, where each face has one screw per row). An M10 A4-70 screw holds about 9,100 lb; the aluminum threads in the boss hold about 4,900 lb on the first 1/4" alone. That is about 6x on the 5x7 and about 3x on the corners. M8 would also pass (about 4.8x on the 5x7); M10 was chosen so the whole system uses one screw.
  • Clearance: the screws sit 5/8" from the post center line, clear of the bolt slots (1-3/4" out) and the lock holes.

Pick a flange, or All flanges to see every condition side by side. The post is see-through so the screws and bosses show. Exploded pulls the screws and the post apart.

Rough numbers for comparing options, not an engineer's stamp. Orange = M10 post screws, blue = 1/2" bolts in the slots, green = lock screws.

Wood framing (deck, balcony or floor edge)

Concrete slab edge

Interactive models: drag to rotate, pinch or use the zoom buttons, two-finger or right-drag to pan. Each shows the same layout against a house wall (deck, balcony or landing): two outside corners, an inside corner, middle posts, an end post at the wall and an open end post. Orange = front face bolts, blue = side face bolts.

Corner Posts

Corner posts carry load from two directions, and on cable railing they carry the cable pull from both runs. They always get the heavier details.

Wood corners: one post

On wood, both outside and inside corners use a single post on a compact one-piece corner flange. It needs only two layers of wood behind it: the fascia and the rim. No extra blocking at the corner, because the corner itself braces the rim.

  • Outside corner flange: about 5" per leg and 7" tall, with the post right on the corner. One 1/2" bolt per face in a vertical slot (1" of travel, centered at mid-height) with a lock screw below it, 4-1/4" from the corner.
  • Inside corner flange: about 3-3/4" per leg and 7" tall. One 1/2" bolt per face in a vertical slot with a lock screw below it, 3" from the corner. The two bolts point away from each other, so they never meet.
  • Backing: the same 1-1/2" x 6" x 1/4" stainless steel (316) strip used on every post, set upright behind the rim with the bolt through its center hole. It spreads the load over the wood far better than a washer and keeps the corner compact.
  • Through-bolt the fascia and the rim (3" of wood) with 1/2" stainless steel (316) bolts.
  • Outside corner distance rule: the bolts must be at least the fascia plus rim thickness plus 1" from the corner. With a standard 1-1/2" fascia over a 1-1/2" rim, that is 4". A thicker fascia or a doubled rim moves the bolts out by the same amount.
  • Tie the corner together. Make sure the rim and the end joist are well fastened to each other at the corner, and add a tension hold-down at the corner. Corner posts carry cable pull from both runs.
  • Two separate posts also work at outside corners, using the same layout as the concrete corner below.
  • Surface mount corners: the same 4" square flange, with the added board 3 run into the corner on both edges. See Surface Mount: Every Condition.

Concrete outside corners: two posts

On a concrete slab edge, a single corner post does not leave room for the anchors: anchors drilled from the two faces cross inside the slab, right at the weakest spot. The clean solution is two posts, one on each face, set close enough that the corner gap stays under 4".

  • Set each post 2" from the slab corner. The diagonal gap between the posts is then about 3-3/8", under the 4" sphere rule.
  • Keep the anchors away from the corner. Use a corner flange with the post at the corner end and both anchors beyond the post, about 4-3/4" and 8-1/4" from the corner.
  • Keep the anchors from the two faces apart. On one face, drill the full 4-1/2" embedment. On the other face, set the anchors 1" lower and drill 3-1/2" deep. The closest rods then clear each other by about 1-5/8". The slotted end flange takes up the 1" difference: face one uses the top of the slot, face two the bottom, so both flanges and posts stay at the same height.
  • Have corners checked. Anchors near a slab corner have two free edges and the least concrete around them. On commercial work, have the engineer confirm the corner layout, or surface-mount the corner posts.

Direct Mount: Screws Through the Post (Stairs and Tight Spots)

For stairs, stringers, lofts and tight spots where a flange will not fit, the post can be screwed straight to the framing with no flange. This is a common option across the industry. It is the light-duty choice: the flanges above remain the engineered mount for outdoor decks and commercial work.

  • Field drilled, to suit the framing. The post ships undrilled (order it taller if needed). The installer cuts it to length and drills it on site, so it fits stair stringers, 2x8 to 2x12 rims and raked posts.
  • How it holds: when the rail is pushed out, the post pivots on its bottom end against the framing and the top screw does most of the work. When the rail is pushed in, the post pivots at the top and the bottom screw holds it. So the top screw goes as high as possible and the post bottom as low as possible.
  • Drilling rules: 5/16" holes through both walls, through the corner bosses, with hole centers 1/2" from the post edges (1/8" inboard of the boss center) so the screw head sits flat, clear of the rounded corner. Alternate sides on a diagonal. Top screw about 1-1/2" below the top of the stringer or rim. Bottom screw at least 2" above the post bottom, clear of the end-cap screws in the bosses. Post bottom as low as the framing allows, flush with the bottom of the stringer or rim. The hole crosses the 1/4" core of the boss, which is fine.
  • Number of screws: 2 minimum. 3 to 4 on stringers or rims 9-1/4" deep or more, alternating sides.
  • Rough pull on the top screw (200 lb at 42", two screws, post bottom flush with the bottom of the framing): about 1,750 lb on a 2x8 rim, 1,350 lb on a 2x10, 1,100 lb on a 2x12 stringer. Deeper framing helps a lot.
  • No sleeve needed. Posts from other makers need a spacer sleeve so the screw does not crush the tube. Our bosses are solid under the head (about 3/8" of aluminum) and the back boss sits flat on the framing, so the post is its own spacer.
  • Screws: Simpson Strong-Drive SDWS Timber SS, Type 316 stainless, 0.276" shank, 0.650" flat washer head, T-50 drive, 3" of thread. Use 6" long with no spacer or the 1" spacer, and 8" long with the 1-1/2" spacer. Simpson's literature compares this screw favorably to 1/2" and 5/8" lag screws.
  • Why not 3/8" lag screws: a 3/8" lag with its 20 mm washer is wider than the boss. Centered on the boss (3/8" from the edge) it hangs past the side of a 2" post. A 1/2" lag is bigger still.
  • Caps: black cap over each screw head.
  • Framing: at least 3" of solid wood for the screw threads (stringer, rim or header plus blocking), the same blocking rules as above. Not for composite, PVC or trim boards.
  • Strength: Simpson lists about 204 lb per inch of thread in withdrawal (about 600 lb for 3" of thread), well under the pull above, so a direct-mount post does not reach the 200 lb guard load with the same margin as a flange. Use it where a flange cannot fit, use more screws where the framing allows, and have an engineer confirm it for guards.
  • Optional drill guide (later): a clamp-on aluminum block with holes on the boss positions, so every installer drills the post the same way.

Deck Board Overhang

Deck boards usually overhang the fascia by 3/4" to 1-1/2". A post or flange mounted flat on the fascia hits the board edge. Two ways to clear it:

  • Option A, notch the deck board (cleanest): cut the overhang to the outline of the post or the 10 mm flange, plus about 1/8" clearance, so the post sits tight to the fascia. No extra parts. Works for direct mount and for every fascia flange.
  • Option B, fascia standoff spacer: when the decking cannot or should not be cut. See below. For the fascia flanges, notching is the standard for now.

Fascia Standoff Spacer (Direct Mount)

  • What it is: a solid aluminum bar, 2" wide to match the post, about 8" tall (longer to order for 3 to 4 screws), set between the post and the fascia so the post clears the deck board overhang.
  • Two thicknesses: 1" and 1-1/2", covering most overhangs.
  • Holes: drilled on site through the post holes, so they always line up. The same screws pass through the post, the spacer and into the framing (longer screws, see above).
  • Material and finish: 6061 aluminum rectangle bar (2" x 1" and 2" x 1-1/2" are standard US stock), cut and drilled in house, powder coated matte black in batches to match the post.
  • Why one bar and not two small pucks: it looks cleaner, spreads the load, stops the post from twisting, and there is only one piece to line up.
  • Note: the spacer adds leverage on the screws. With the 1-1/2" spacer, use the 8" screws, or 1/2" through-bolts where the back can be reached.

Waterproofing Around Post Mounts

Every bolt, lag or anchor hole is a path for water. This matters most on roof decks and balconies with a waterproof membrane and a living space below.

  • Fill every hole with sealant before the fastener goes in, so the sealant fills the hole and seals around the threads.
  • Seal the underside of the flange and under each washer and nut. Polyurethane sealant is a common choice. Check that it is compatible with the membrane, since not every sealant bonds to every membrane.
  • Fascia mounts: apply self-adhered flashing tape over the fascia and rim where each post mounts, so the bolts pass through a sealed layer.
  • Surface mounts on a membrane: follow the membrane maker's detail for penetrations. Drilling through a membrane can affect its warranty, so check with the installer or maker first.

Stairs and Inclined Mounts

  • On a stringer or a 2x wall plate, a pivot flange's two holes end up along the rail line. Through-bolt into the stringer with blocking where possible, or add a cross block so the holes can run across the rail.
  • Tight stairs and stringers: the post can also be screwed straight to the stringer with no flange. See Direct Mount.

Cable Railing: What's Different

Ready to plan your cable railing? See Cable Railing Systems & Complete Prices.

V4 Parts List

New and changed parts for the V4 post system. Names marked * are working names, not final SKUs yet.

SKU Part Status
Surface flanges
FLG.SUR.4.00.BLK Square surface flange, 4" x 4" x 3/8", 8 holes on a 1-1/2" pitch (corners 7/16", middles 9/16"), 4 x M10 post holes Replaces FLG.FLR.3.75.BLK
FLG.SUR.SLM.3.75x2.50.BLK * Slim surface flange, 3.75" x 2.5" x 3/8", 4 x 7/16" holes New, premium, load test first
FLG.SUR.SLM.L.3.75.BLK * Slim L corner flange, 3.75" L, 2.5" legs; turned 180° for inside corners New, premium, load test first
Base covers (1-1/8" tall, 1.2 mm wall)
BC.SQU.4.13.BLK Square cover, 105.0 mm Replaces BC.SQU.3.88.BLK
BC.SLM.3.88x2.63.BLK Slim cover, 98.7 x 66.9 mm New
BC.SLM.L.3.88.BLK Slim L corner cover, 98.7 mm L, 66.9 mm legs New
Fascia (side-mount) flanges, slotted
FLG.FSC.5x7.BLK * Standard fascia flange, 5" x 7" x 10 mm, 2 slots 9/16" x 1-9/16" (3-1/2" apart) + 2 lock holes 17/64" + 4 x M10 countersunk post holes New
FLG.FSC.CRN.OUT.BLK * Wood outside corner, one piece, legs about 5", 7" tall, 1 slot + 1 lock hole per leg + 8 x M10 countersunk post holes (4 per face) New
FLG.FSC.CRN.IN.BLK * Wood inside corner, one piece, legs about 3-3/4", 7" tall, 1 slot + 1 lock hole per leg + 8 x M10 countersunk post holes (4 per leg) New
FLG.FSC.END.BLK * Concrete end flange, post at one end, both anchors beyond it (concrete end posts and outside corners); 2 slots 9/16" x 1-9/16" + 2 lock holes 17/64", same as the 5x7, + 4 x M10 countersunk post holes New, final size not set
Backing and hardware
BKG.STRIP.1.5x6.316 * Backing strip, 1-1/2" x 6" x 1/4" 316, three 9/16" holes New, one part for all wood fascia
HW.FSC.WOOD.KIT * 1/2" 316 through-bolts, washers, nuts, backing strip, #14 316 lock screws, M10 x 30 316 flat-head post screws New kit
HW.FSC.CONC.KIT * 1/2" 316 threaded rod, nuts, washers, concrete lock screws, M10 x 30 316 flat-head post screws (adhesive anchoring) New kit
HW.SUR.WOOD.KIT * 4 x 3/8" x 8" 316 lags + washers New kit
HW.SUR.CONC.KIT * 1/2" 316 slim washer (7/8" OD) + 1/2" 316 jam nut New kit
Direct mount (screws through the post)
Standard 2x2 post Same post, shipped undrilled (taller if needed); the installer cuts and drills it on site per the drilling rules No new part
SPC.FSC.1.00.BLK * Fascia standoff spacer, 2" x 1" x about 8", 6061 aluminum, undrilled (drilled on site through the post holes), powder coated black New, drawing next
SPC.FSC.1.50.BLK * Fascia standoff spacer, 2" x 1-1/2" x about 8", same as above New, drawing next
HW.DM.WOOD.KIT * 2 x Simpson SDWS Timber SS 316 screws (0.276" x 6", or x 8" with the 1-1/2" spacer) + 2 black caps; add screws for 3 to 4 per post New kit
DG.DM.2x2 * Optional clamp-on drill guide, aluminum block with holes on the boss positions Later

Unchanged: pivot flange (stairs), post brackets, post end cap, handrail splines and end cap. Dropped: FLG.FLR.3.75.BLK, BC.SQU.3.88.BLK, PLT.CRN.WOOD.2.5. Not designed yet: concrete inside-corner fascia flange; a stair version of the fascia flange if needed.

V4 Manufacturing Drawings (Rev 4)

One drawing per part, on the Inline Design sheet: inches with millimeters in brackets, ordinate dimensions, hole callouts, notes, third angle projection, revision 4. Generated 2026-09-27. Each link opens the PDF.

Still to draw: the two standoff spacers and the optional drill guide.

Open Decisions

  • Drill guide: make it now or later.
  • Final SKU names for the spacers, the screw kit and the drill guide (working names marked * above).
  • Whether the fascia flanges also need a standoff spacer, or notching the deck board stays the standard.
  • Black caps for the direct-mount screw heads: pick the part.

Maintenance

  • After the first season (about 6 to 12 months): retighten every fascia bolt. New lumber, especially pressure-treated, shrinks as it dries and the bolts lose their grip. Snug each nut until the washer and backing strip sit tight against the wood, without crushing it.
  • Every year after that: push on the top rail at each post. If a post moves, retighten its bolts.
  • Lock screws: check they are still tight. They keep the fascia flange at its height, but they do not replace tight bolts.
  • Surface flanges on wood: check the lags the same way.
  • Concrete: check that the anchor nuts are tight and the rods or studs have not loosened.
  • Cable railing: check cable tension at the same time. Posts that move and slack cables usually show up together.

A Note on Codes

These are industry best practices, not a site-specific engineering design. Check with your local building department, and consult a licensed engineer where required.