Frame Fixings: The Right Way to Secure Window and Door Frames
How frame fixings work, which type to use, and why overtightening is the single biggest installation mistake. Nylon frame fixings vs concrete screws, spacing rules, length selection, and UK pricing.
A uPVC window that won't open properly six months after installation. The frame has bowed inward by 3mm along one jamb, just enough to bind the sash. The cause isn't the window. It's the fixings. Someone cranked them tight without packers behind the frame, pulled the profile hard against uneven masonry, and walked away. The frame looked fine on the day. It doesn't look fine now.
Frame fixings are one of the simplest components on a window or door installation. A long screw, a method of gripping masonry, and a head that sits flush. But the way they're installed determines whether that frame stays straight for twenty years or slowly distorts until nothing opens, closes, or seals the way it should.
What frame fixings are
A frame fixing is a long screw designed to pass through a window or door frame and anchor into the masonry behind it. The traditional type has an integral nylon plug built around the screw shaft. You drill a hole through the frame and into the wall, push the whole assembly through, and drive the screw. As the screw tightens, the nylon sleeve expands inside the masonry hole and locks the fixing in place. One operation, one component, one hole.
That's the key advantage over the old method of drilling the wall separately, hammering in a plastic wall plug, then screwing through the frame into the plug. Frame fixings let you drill with the frame sitting in its final position, which means the hole in the frame and the hole in the wall line up perfectly every time.
The screw heads are designed to sit flush with (or just below) the frame surface. Countersunk heads for timber and uPVC frames. Pan or hex heads for aluminium and steel frames where the fixing goes through a pre-formed channel.
Types of frame fixing
Two types dominate the UK market. They solve the same problem differently, and the right choice depends on your masonry.
Nylon frame fixings
The traditional option. A steel screw inside a nylon sleeve that expands when driven. Fischer SXR and DuoXpand are the names you'll see most often. Rawlplug KKS-R is the main alternative. These work in brick, block, concrete, and stone. The expansion mechanism means they grip reliably even in slightly oversized holes or softer substrates like lightweight block.
The screw can be backed off and re-driven without losing grip, which matters during installation. You need to adjust the frame position after initial fixing? Loosen the screw, repack, re-tighten. Try that with a concrete screw and the thread channel in the masonry is already cut, so the second bite is weaker.
Typical diameters: 8mm and 10mm. Typical lengths: 80mm to 160mm. Pack sizes from 4 to 50.
Concrete screws (masonry screws)
The newer option, and the one gaining serious ground. A hardened steel screw with aggressive threads that cut directly into masonry without any plug. Drill a 6mm pilot hole, drive the 7.5mm screw straight in. Faster, cheaper per unit, and fewer components.
Screwfix's Easydrive range is the dominant own-brand product here, rated 4.8 out of 5 from over 500 reviews. They work brilliantly in good-quality brick and dense concrete. Where they can struggle: soft mortar joints, lightweight aircrete blocks, and any substrate where the pilot hole crumbles rather than holding clean edges. In those situations, the screw spins without gripping.
| Feature | Nylon frame fixings | Concrete screws |
|---|---|---|
| How they grip | Nylon sleeve expands inside drilled hole | Hardened threads cut directly into masonry |
| Pilot hole | 8mm or 10mm (matches sleeve diameter) | 6mm (for 7.5mm screw) |
| Adjustability | Can loosen and re-tighten without losing grip | Re-driving weakens the thread channel |
| Best substrate | All masonry types including lightweight block | Dense brick and concrete |
| Worst substrate | None, though overkill for dense concrete | Soft mortar, aircrete, friable block |
| Unit cost (approx) | £0.40-1.40 each depending on brand | £0.13-0.26 each in 100-packs |
| Typical pack | 4-50 fixings | 10-100 fixings |
| Brand leaders | Fischer DuoXpand, Fischer SXR, Rawlplug KKS-R | Easydrive (Screwfix), Toolstation own-brand |
The community consensus from trade forums is clear: concrete screws for straightforward installations into good masonry. Nylon frame fixings when you're not sure what's behind the plaster, when the masonry is soft or uneven, or when you need maximum adjustability during installation.
Head types
Countersunk heads sit flush with the frame surface. Use these for timber and uPVC frames where the screw drives directly through the frame material. The head pulls down into the profile and disappears.
Pan head and hex head fixings stand proud of the surface. These are used with aluminium and steel frames where the fixing passes through a dedicated channel or clip, and the head bears against a washer or retaining plate rather than the frame material itself.
For most domestic window and door installations in the UK (uPVC or timber frames into brick or block), countersunk nylon frame fixings or countersunk concrete screws are what you need.
How to install frame fixings
This is where the money is. Get the installation sequence right and your windows and doors will work perfectly for decades. Get it wrong and you'll be re-hanging frames within a year.
Choosing the right length
The fixing must pass through three zones: the frame profile, the gap between frame and masonry, and into the masonry itself. The GGF (Glass and Glazing Federation) specifies a minimum 40mm embedment into masonry for plugged fixings, and 25mm into timber substrates.
The formula is simple:
Frame profile depth + gap to masonry + 40mm = minimum fixing length
A standard uPVC window profile is 60-70mm deep. The gap between frame and reveal is typically 5-15mm (filled with packers and sealed). So: 65mm frame + 10mm gap + 40mm embedment = 115mm minimum. Round up to the next available size: 120mm fixings.
For deeper frames, wider gaps, or situations where you want extra security, go longer. There's no penalty for 20mm of extra embedment. There is a real penalty for 10mm too little.
Spacing rules
BS 8213-4:2016 and the GGF Good Practice Guide set out the spacing requirements. These aren't suggestions.
Timber and uPVC frames:
- 150-250mm from each corner (measured from the external corner of the frame)
- Intermediate fixings at no more than 600mm centres
- Minimum two fixings per jamb
Aluminium frames:
- 100-150mm from each corner (tighter spacing than timber/uPVC)
- Intermediate fixings at no more than 600mm centres
Head fixings (across the top of the frame):
- Frames up to 1200mm wide: no mechanical fixing needed at head if foam-fixed
- 1201-2400mm wide: one central head fixing
- 2401-3600mm wide: two equally spaced head fixings
One thing to watch: some installers avoid fixing through the head entirely because of the lintel above. If there's a steel or concrete lintel directly behind the head of the frame, drilling into it risks hitting reinforcement or cracking the concrete. Check what's behind the plaster before you drill. If it's a lintel, foam-fix the head and put your mechanical fixings in the jambs and sill only.
The installation sequence
This sequence applies whether you're using nylon frame fixings or concrete screws. The order matters.
Position the frame in the opening
Sit the frame on packers at the sill. Use plastic frame packers (not offcuts of wood, which absorb moisture and rot). The packers set the frame height and create the gap needed for sealant underneath.
Check plumb and level
Use a spirit level on both jambs (plumb) and the head and sill (level). Adjust packers until the frame is true. This is your reference position. Everything that follows aims to hold the frame in exactly this position.
Pack behind every fixing point
This is the step people skip, and it's the step that causes 90% of frame distortion problems. Before you drill a single hole, place a packer between the frame and the masonry at every point where a fixing will go. The packer must span the full depth of the outer frame. It creates a solid bridge so that when you tighten the fixing, the frame bears against the packer instead of being pulled into a void.
Drill through the frame into the masonry
Always drill with the frame in position. Do not pre-drill the masonry holes separately and then try to line them up. Use an SDS drill with the correct diameter bit (6mm for 7.5mm concrete screws, 8mm or 10mm for nylon frame fixings depending on the product). Drill through the frame and into the masonry in one pass to the required depth.
Insert fixings finger-tight only
Push the fixing through and drive the screw until it's just snug. Not tight. Not even close to tight. The fixing should hold the frame in position but allow slight movement if you tap the frame with your hand.
Recheck plumb and level
The act of drilling and inserting fixings can shift the frame slightly, especially in uPVC where the profile flexes. Check plumb and level again after every pair of fixings. Adjust packers if needed.
Progressive tightening
Once all fixings are in and the frame is confirmed plumb and level, go back and tighten each fixing progressively. A quarter turn at a time, working around the frame, checking plumb and level as you go. Stop tightening when the fixing is firm. Not when the screw stops turning. Not when the drill clutch clicks. When it's firm.
The packer-fixing relationship
Think of every fixing point as a pair: one fixing, one packer. The packer sits between the frame and the masonry. The fixing passes through the frame, through the packer, and into the masonry. When you tighten the screw, the packer prevents the frame from being pulled inward.
Without a packer, the fixing pulls the frame toward the masonry at that point. The frame bows inward between the fixing points, creating a curve that's almost invisible at first but gets worse over time as the uPVC creeps under constant stress. The window or door sash starts to bind. Seals compress unevenly. Draughts appear. Water gets in.
Packers must be plastic, not wood. They need to resist compression, rot, and moisture. Standard plastic frame packers come in various thicknesses (1mm, 3mm, 5mm, 10mm) and can be stacked to fill any gap size. They cost almost nothing. A bag of 200 mixed packers runs about TBC.
How many do you need
A standard window (1200mm x 1200mm) needs roughly 8-10 frame fixings: two per jamb plus one or two at the head, plus sill fixings if applicable. Larger windows need more.
For a typical three-bedroom house with 8 windows and 2 external doors, you're looking at 80-120 fixings in total. That's one or two trade packs of concrete screws, or two to three packs of nylon frame fixings.
Bifold doors and large sliding doors need more fixings because the frames are longer and carry more weight. A 4-metre bifold track frame will need fixings at 150mm from each end and then every 400-500mm along its length, plus additional fixings at every panel junction point. Budget 15-20 fixings for a single bifold installation.
Buy 20% more than your count. You'll break one drilling into hard masonry, strip one in a soft mortar joint, and want spares for the fixing that doesn't quite grip and needs relocating 50mm along.
Cost and where to buy
Frame fixings are cheap. The fixings themselves will never be a meaningful line item on your project budget. What matters is buying the right type and having enough of them.
Concrete screws (7.5mm countersunk, Torx drive):
Easydrive 7.5 x 100mm (100 pack) at Screwfix: TBC. That's roughly 20p per fixing. The same screws in 80mm run TBC, in 120mm TBC, and 150mm TBC. Toolstation's own-brand masonry screws are slightly cheaper: 7.5 x 102mm (100 pack) at TBC.
Small packs (10 fixings) are available from about TBC at Toolstation for longer lengths. Useful if you're doing a single window.
Nylon frame fixings (branded):
Fischer DuoXpand countersunk 8 x 120mm (10 pack): TBC. That's about TBC per fixing. The hex head version: TBC. Fischer SXR-L trade packs (50 fixings) range from TBC for 8 x 100mm up to TBC for 10 x 160mm.
Rawlplug KKS-R 8 x 100mm (16 pack): TBC. The 10mm diameter versions in 50-packs: around TBC.
Budget nylon frame fixings (Screwfix Easyfix or Toolstation own-brand) come in at TBC for a 50-pack. They work. They're just not as adjustable or forgiving as Fischer.
The unit cost difference is stark. Concrete screws at £20 each versus Fischer DuoXpand at TBC each. For a whole-house window installation needing 100 fixings, that's £20 versus £20. The premium is justified when your masonry is questionable. It's wasted money when you're fixing into solid engineering brick.
Both Screwfix and Toolstation carry the full range. Stock levels are good; these are high-volume products. There's no reason to order online and wait unless you need a specialist length or stainless steel finish for coastal exposure.
Alternatives to frame fixings
Traditional plug and screw
The old method. Drill the masonry, insert a wall plug, position the frame, drill through the frame, and drive a wood screw through the frame into the plug. It works. People fitted windows this way for decades. But it requires two separate drilling operations and precise alignment between the frame holes and the plug holes. With frame fixings, you drill once through both.
The plug-and-screw method still has a place for timber sub-frames where you're screwing into wood rather than masonry, or for situations where the masonry is too damaged or irregular for frame fixings to grip.
Mechanical brackets and straps
Metal fixing straps screwed to the back or side of the frame and then screwed or plugged into the surrounding masonry. Common with pre-glazed windows where you can't remove the glass to access the frame for through-fixing. The strap bends around the edge of the frame and fixes to the reveal.
Straps cost about TBC per window. They're perfectly adequate for standard domestic installations and are the method specified by several uPVC window manufacturers for their pre-glazed units. The downside: less adjustability than through-frame fixings, and you need to plaster or cover the straps afterward.
For bifold and sliding door systems, mechanical brackets are often specified by the manufacturer rather than through-frame fixings. Always check the installation manual. Using the wrong fixing method can void the warranty.
Where you'll need frame fixings
Windows and doors are the primary application. Every window and external door frame on your project needs frame fixings (or an approved alternative bracket system). Internal doors are fixed differently, typically with screws into timber linings.
Bifold and sliding doors need frame fixings along the full length of the outer frame, including the head track and threshold. These are larger, heavier frames carrying more weight, so fixing spacing is tighter (typically 400-500mm centres rather than 600mm) and embedment depth is greater. Follow the manufacturer's specific requirements; they vary between systems.
Curtain walling and large glazed screens use specialist fixing systems beyond the scope of standard frame fixings. If your project involves structural glazing, that's a specialist installer's territory.
Garage door frames are sometimes fixed with frame fixings, though coach bolts or expanding anchors are more common for the heavier frames used with up-and-over and sectional doors.
Common mistakes
Overtightening
The number one problem. It comes up in almost every forum thread about window installation. Frame fixings are not structural bolts. They don't need to be torqued to a specification. They hold the frame in position against wind load and prevent the frame from being pushed out. That's a lateral (shear) load, not a pull-out load. The fixings are there to stop the window falling out, not to clamp it against the wall.
Overtightening pulls the frame inward between the fixing points, creating a bow. On a uPVC frame, even 1-2mm of bow is enough to affect how the window opens and closes. The frame profiles have relatively thin walls and limited resistance to distortion. Tighten until firm, then stop.
If you're using a cordless drill to drive frame fixings, set the clutch to its lowest setting. Better still, use a hand screwdriver for the final tightening. The torque from a drill driver can pull a uPVC frame out of true before you feel any resistance in your hand. Once the frame is distorted, loosening the fixing doesn't always let it spring back. The damage can be permanent.
Wrong length
Too short means insufficient embedment. The fixing holds initially but works loose over time as wind load cycles the screw back and forth in too little masonry. The GGF minimum is 40mm into plugged masonry holes. Measure your frame depth, measure your gap, add 40mm, and round up.
Too long is rarely a problem, but watch for fixings that pass all the way through a single-leaf wall or into a cavity. You don't want a frame fixing bridging the cavity and touching the inner leaf.
Too few fixings
Skipping the intermediate fixings because "two per side should be enough" leaves the middle of each jamb unsupported. The frame flexes inward under wind pressure, breaking the seal between frame and masonry. On tall windows (over 1200mm), you need at least three fixings per jamb.
Not checking plumb before final tightening
Driving all the fixings tight in one pass without rechecking plumb and level between each pair. The frame shifts slightly with each fixing. By the time you've done all eight, the frame can be 3-4mm out of plumb, and every fixing is now holding it in the wrong position. Check after every pair. Adjust before the next pair. It takes an extra five minutes and saves you from a strip-out.
Skipping packers
Already covered in detail above, but it bears repeating: no packer behind a fixing point means the frame will distort when you tighten the screw. Every fixing needs a packer. No exceptions.
Drilling into mortar joints instead of brick
Frame fixings need solid substrate. Mortar joints are softer, more variable, and more likely to crumble when drilled. Aim for the brick or block face. If a fixing position lines up with a mortar joint, move it 30-40mm to hit solid masonry. The spacing rules give you enough tolerance for this kind of adjustment.
Getting it right
Frame fixings are forgiving if you follow the sequence: position, pack, check plumb, drill in situ, fix finger-tight, recheck, tighten progressively. Skip any step and you're relying on luck.
The fixing itself costs pennies. The packer costs less. The spirit level check takes thirty seconds. None of this is expensive or difficult. What's expensive is re-hanging a window because the frame was pulled out of true by someone who treated a frame fixing like a coach bolt and cranked it until the drill stalled.
Buy decent fixings. Fischer or Rawlplug if your masonry is uncertain. Easydrive concrete screws if it's solid brick. Pack behind every fixing point. Check plumb twice. Tighten once, gently. That's the whole job.