Fitting Skirting Boards and Architrave: Methods, Joints and Fixings

Quick Answer: Skirting boards are fitted with internal corners scribed (not mitred) and external corners mitred at 45°, joined on long walls with a 45° scarf joint, and fixed at roughly 600mm centres into studs/blockwork with 50–63mm screws or 50–63mm second-fix nails plus grab adhesive. Architrave is fitted with a consistent margin/reveal of 5–8mm around the frame, mitred at 45° at the head corners, and pinned with 38–50mm lost-head or brad nails. This is second-fix carpentry; good practice follows BS 8000-5 for workmanship and BS EN 942 for joinery timber quality.

Summary

Skirting and architrave are the trim that frames a room — and because they sit at eye level and run the length of every wall, sloppy joints are instantly visible. They are the classic second-fix carpentry job: quick to do badly, surprisingly skilled to do well. The two recurring tests are the scribed internal corner on skirting (a mitre on an internal corner opens up as the timber moves and as walls go out of square) and the clean 45° mitre on architrave heads.

The job is dominated by the fact that nothing in a real house is straight or square. Walls bow, internal angles are never a true 90°, floors slope, and frames sit proud or shy of the plaster. A good trim carpenter works to the reality on site — scribing internals so they close tight regardless of the wall angle, setting a consistent architrave margin even when the frame isn't, and packing behind boards over bowed walls so the face line stays true.

This guide covers measuring and ordering, the correct joints (scribe, mitre, scarf), fixing methods into different backgrounds, setting architrave margins, and dealing with the imperfections you'll always meet. It assumes a chop saw or mitre block, a coping saw, and a second-fix nail gun or pins and adhesive.

Key Facts

Quick Reference Table

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Joint / detail Method Typical cut
Internal corner (skirting) Scribe one piece to profile of other Square cut + coped profile
External corner (skirting) Mitre 45° each piece
Joining skirting on a long wall Scarf joint 45° opposing cuts, glued
Architrave head corners Mitre 45° each leg
Architrave to skirting (foot) Square butt onto skirting 90°
Architrave margin Consistent set-back from frame 5–8mm reveal
Skirting fixing centres Into studs / regular spacing ~600mm
Skirting fixing Screw + plug / 2nd-fix nail + adhesive 50–63mm
Architrave fixing Lost-head nail / brad 38–50mm

Detailed Guidance

Measuring, Ordering and Setting Out

Measure each wall and add up totals, then add a sensible waste allowance — typically 10–15% for scribes, mitres and cutting errors, more on a room with lots of short returns. Order skirting in the longest lengths that will fit the room and your transport, to minimise scarf joints on long runs.

Plan the order of fitting before cutting. The principle for skirting: fit the wall opposite the door first with both ends square (it sits between two walls), then work around the room scribing each subsequent piece into the one already fixed. The last piece into a corner is the scribed one. Mark stud positions on the floor or wall before you start so you know where your fixings will bite.

Scribing Internal Corners (Skirting)

Internal corners must be scribed, not mitred. A mitre on an internal corner relies on the wall being a perfect 90° (it never is) and opens into an ugly gap as the timber shrinks. A scribe cuts the end of one board to the exact reverse profile of the moulding it butts against, so it closes tight regardless of the wall angle.

Method:

  1. Cut and fix the first board with a square end hard into the corner.
  2. On the second board, cut a 45° internal mitre as if you were going to mitre the corner — this exposes the moulding profile as a pencil line along the cut face.
  3. With a coping saw, cut along that profile line, undercutting slightly (back-bevel ~5°) so only the front edge touches.
  4. Offer it up against the first board — it should nest tightly over the moulding. File/sand the profile to fine-tune.

A well-cut scribe stays tight even when the wall angle is 92° or 87°. For tall or intricate mouldings, some carpenters power-scribe with a router or use a multi-tool, but the coping saw remains the on-site standard.

Mitring External Corners and Scarf Joints

External corners (e.g. around a chimney breast) are mitred at 45°. Because external wall angles are rarely exactly 90° either, check the actual angle with a sliding bevel/angle finder and split it — if the corner is 92°, cut each piece at 46°. Glue the mitre faces and pin through the joint to lock it; a tight, glued external mitre won't open.

To join skirting along a long wall, use a scarf joint — two opposing 45° cuts that overlap — not a square butt joint. The scarf gives a longer glue surface, hides timber movement, and is far less visible than a butt line. Position scarf joints over a stud where possible so both pieces are fixed solidly, and glue the joint.

Fixing Skirting to Different Backgrounds

Fix at roughly 600mm centres, ideally into studs (mark them first). Method varies by background:

Countersink and fill screw/nail heads. Leave a hair gap at the top and run flexible decorator's caulk along the top edge before painting to mask wall undulation and movement — never rigid filler, which cracks.

Fitting Architrave: Margins and Mitres

Architrave frames the door lining. The key to a professional look is a consistent margin (reveal) — the small set-back of the architrave from the inner edge of the frame, typically 5–8mm. Set it the same all the way round.

Method:

  1. Use a combination square or marking gauge to pencil the margin line on the face of the frame on both legs and the head.
  2. Cut and fit the two legs first, standing on the floor (or on the skirting), with the inner edge on the margin line; cut a 45° mitre at the top of each leg.
  3. Cut the head to span between the two legs with a 45° mitre at each end, so the mitres meet cleanly at the top corners.
  4. Glue the mitres and pin through the corner (a nail through the head into the leg) to stop the mitre opening.
  5. Pin each leg with two fixings per point — one into the frame, one into the wall stud where reachable — at intervals up the leg.

Where architrave meets skirting at the floor, the architrave usually runs to the floor and the skirting butts square against it (or sits behind it if the architrave is thinner). Plan which sits proud so the junction is neat.

Dealing with Out-of-Square and Imperfections

Real rooms fight you. The fixes:

Frequently Asked Questions

Should I scribe or mitre internal skirting corners?

Always scribe internal corners. A mitre on an internal corner depends on the wall being exactly 90° — which it never is — and opens into a visible gap as the timber moves and the room settles. A scribe cuts one board to the exact reverse profile of the other so the joint stays tight regardless of the wall angle. External corners, by contrast, are mitred at 45°.

What's the standard margin for architrave?

A consistent 5–8mm reveal (set-back) from the inner edge of the door frame all the way round — legs and head the same. Mark it with a combination square or gauge before fitting. The eye reads the evenness of the margin, so keeping it identical on both sides and across the head is what makes the finish look professional, even if the frame itself isn't perfectly plumb.

How do I fix skirting to a wall with no studs in the right place?

On masonry, screw and plug (drill, insert plug, countersunk screw) at ~600mm centres. On dry-lined or stud walls where studs aren't where you need fixings, use a strong grab adhesive along the back of the board combined with second-fix nails into whatever timber is available. For bowed walls, pack behind the high points so the face stays straight and let the adhesive bridge the gaps. Always fill and caulk before painting.

Why does my architrave mitre keep opening up?

Either the mitre wasn't cut at a true 45° (or the corner isn't 90° and needs splitting), or it wasn't glued and pinned. Always glue the mitre faces and drive a pin through the corner — a nail through the head into the top of the leg — to lock the two pieces together. Timber movement and knocks open un-pinned mitres over time; a glued, pinned mitre stays shut.

MDF or softwood skirting and architrave — which is better?

MDF is dimensionally stable, won't warp or have knots, takes paint beautifully, and is the default for painted trim — predrill near ends to avoid splitting and seal cut edges before painting. Softwood (redwood/pine) is preferred where a stained or natural finish is wanted, or for heritage work, but moves more with humidity and may have knots that need treating. For most modern painted interiors, moisture-resistant MDF is the practical choice; use moisture-resistant grade in bathrooms.

Regulations & Standards