What size uPVC window fixing lugs do I need? (And how many per window?)
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uPVC window fixing lugs, cleats and brackets are three names for the same part: a galvanised steel strap that clips into the back of a window or door frame and screws to the wall, so you fix the frame without drilling through its face. The standard size is 202mm long by 20mm wide. Most domestic windows need 8 to 10 lugs; fix down each jamb first, 150mm from each corner and no more than 600mm apart.
What is a window fixing lug (and why is it also called a cleat or a bracket)?
A fixing lug is a flat galvanised steel strap. One end has a lip or tang that hooks into the groove on the back of a uPVC frame; the other end sits against the brick or block reveal, and you drive a screw through it into the wall. The frame is then held from behind, so the front face stays clean with no screw caps to fit and no filling.
You will hear the same part called a lug, a cleat, a fixing bracket or a frame cramp depending on who is doing the ordering. They are the same thing. That is worth knowing, because search results and supplier catalogues split across all four names and you can end up thinking a shop does not stock what it plainly does.
The alternative to lugs is fixing straight through the frame face with a frame screw. That is quicker on new build, but it puts a visible fixing (and a cap) through the frame, and it means drilling through the profile chamber. Lugs are the tidy option, and the standard choice for replacement work where you do not want to touch the frame face.
What size uPVC window fixing lug do I need?
The trade standard is 202mm long by 20mm wide, in galvanised steel. That length is set up to reach from the frame groove across a normal cavity-wall reveal to solid masonry. Our steel frame fixing lugs are 202mm and fit Veka and Rehau 70mm profiles, which covers most uPVC systems fitted in the UK.
You do not usually size the lug to the window. One size does nearly every job. Two things to check before you order:
- Profile. The lip has to seat in the frame groove. 70mm profiles (Veka, Rehau and most systems built on them) are the common case. If you are fitting an older or specialist profile, offer one lug up first.
- Reveal depth. The lug is galvanised steel and bends by hand on site, so a deep or awkward reveal is not a problem. You shape the lug to bridge the gap rather than buying a longer one.
How many fixing lugs do I need per window?
Work it off the frame, not the glass. The rule fitters follow is: a fixing within 150mm of every corner, then intermediate fixings at no more than 600mm apart down each side, and one within 150mm of any mullion or transom where frames join. Fix the two jambs (the vertical sides) as a minimum; add the head and, on wider openings, the cill.
That gives you a count per side you can add up:
| Frame length on that side | Fixings needed on that side |
|---|---|
| Up to 600mm | 2 |
| 601mm to 1200mm | 3 |
| 1201mm to 1800mm | 4 |
| 1801mm to 2400mm | 5 |
So a standard 1200mm x 1200mm window fixed on all four sides works out at 3 + 3 down the jambs and 3 + 3 across the head and cill: around 12 lugs. Fix jambs and head only and you are nearer 8 to 9. A small top-light might take 6; a patio door or a big picture window will be into the mid-teens.
As a quick planning figure, reckon on 8 to 10 lugs for a typical domestic window and count the openings.
What pack size should I buy?
Pack size follows the job. The per-lug price drops as the pack gets bigger, so buy for the whole job rather than per window:
| Pack | Price | Per lug | Covers roughly |
|---|---|---|---|
| Pack of 10 | £8.10 | 81p | One window |
| Pack of 25 | £17.75 | 71p | Two to three windows |
| Pack of 50 | £31.50 | 63p | A full house of five or six openings |
Packs of 5 and 100 are stocked as well. Buying the 50 instead of five tens saves you about 18p a lug, which on a full reglaze is worth having. Prices are correct at the time of writing; check the product page for live pricing. All three come with free UK delivery.
How do you fit uPVC frame fixing lugs?
Step One: clip the lugs to the frame
Before the frame goes in, hook the lugs into the groove on the back of the frame at your marked positions (150mm from each corner, then spaced along). Bend the fixing end square so it will sit flat against the reveal once the frame is in.
Step Two: set the frame and pack it plumb
Stand the frame in the opening on packers and get it level, plumb and square before you fix anything. This is the step people rush. The lugs hold the frame to the wall, but they do not hold it straight; the packers do that. Check the diagonals are equal and that the frame is not bowed in the middle, then keep the packers behind the fixing points so you are not pulling the frame out of line when you tighten up.
Step Three: screw the lugs to the wall
Fold each lug out to the reveal and fix it. Into brick or concrete, a concrete frame screw straight through the lug is fastest and holds well; into soft block or timber, a screw and plug of the right size. Do not overtighten, you only need the frame held firm against the packers. Once every lug is fixed, recheck plumb and square before you foam and seal.
Common mistakes to avoid
- Fixing too far from the corners. A fixing more than 150mm from a corner lets the frame flex there, and that is where the seal fails first.
- Skipping the packers. Lugs plus foam with no packers behind the fixings gives you a frame that looks fixed but moves. Pack it, then fix it.
- Relying on foam to hold the frame. Expanding foam seals and insulates the gap. It is not a structural fixing. The lugs do the holding.
- Overtightening into soft block. Strip the fixing and the lug does nothing. Use the correct plug and stop when the frame is firm.
- Ordering by one name only. If your usual supplier "does not stock lugs", ask for cleats or frame brackets. Same part.
The short version
Buy 202mm galvanised lugs, one size does nearly every uPVC frame. Allow 8 to 10 per window, fixed within 150mm of each corner and no more than 600mm apart. Pack it plumb, screw the lugs to solid masonry, and let the foam seal rather than hold. Browse the full range on our window fixing lugs page, or call the counter if you want to talk a job through.
By Steve, Builders Hardware Direct. Steve runs the BHD trade counter and has spent years supplying fixings to window fitters and builders across South Wales. Questions on a job? Call the counter on 01269 267030 or order online for free UK delivery.
