Boarding an opening does three jobs at once: it stops the weather, it stops anybody climbing in, and it stops the rest of the glass falling on somebody. They need doing in roughly that order of urgency and in exactly the opposite order of effort.
The glass is the dangerous part and the part people rush. The board is the easy part and the part people get wrong.
Glass first
Two kinds of glass behave very differently:
- Toughened glass has already gone. It breaks into a heap of small blunt cubes and there is nothing left to support. Sweep and shovel.
- Laminated glass holds together on a plastic interlayer, so it sags in the frame as a floppy sheet rather than falling. Cut it free with a sharp knife along the frame line, roll it, and be aware the edges are still sharp.
- Old single glazing in a timber sash is the worst case: large sharp shards, often still bedded in hard putty. Take your time.
Leave what is firmly held if the board is going straight over it. Glass that is not moving and will be covered is safer left alone than levered out.
Sweep, then sweep again, then go over it with a damp cloth or a wet mop. Fragments travel several metres, they get into carpet pile and skirting gaps, and they turn up under bare feet a week later. In a room where anybody sleeps on the floor, this matters a great deal.
What to board with
A sheet of 18 mm ply screwed properly into a frame is a serious obstacle. A sheet of thin board tacked on with a few nails is a gesture, and it comes off with one pull.
Polythene is for weather, not for security. Sheet, then batten it down around the edges so the wind cannot get under it, and understand you have made a window out of plastic rather than a wall.
Cut it oversize. At least 50 mm of overlap onto the frame all round, and more if the frame allows. A board that fits neatly inside the opening can be pushed straight through.
Inside or outside
Inside is better where you can do it, for three reasons: the fixings are not exposed to weather, the board is much harder to lever off from outside, and you can work in the dry.
Outside is necessary when the opening is at ground level and you need the room usable, when the frame only presents fixing timber on the outer face, or when the reveal inside is plastered and offers nothing to screw into.
If you board outside, use screws with a head that resists a screwdriver from a casual attacker if you have them, countersink so there is no lip to lever, and consider a second board inside as well on a ground floor opening.
Fixing it so it holds
Screw into the timber frame. That is where the strength is. Old mortar, soft brick and crumbling render will not hold a plug under load, and a fixing that pulls out takes a lump of wall with it.
- Screws, not nails. Nails pull straight out under leverage; screws do not.
- Long enough to bite properly, at least 30 mm into solid timber.
- Every 200 to 300 mm around the perimeter, and not concentrated at the corners.
- Pilot holes near the edge of the board, so the ply does not split.
- Battens across the back of a large opening, so the board cannot be flexed inwards.
Where there is genuinely no timber, a common trick is a batten cut slightly longer than the opening, wedged inside the reveal, with the board screwed to that. It is not as strong and it is far better than nothing.
Do not screw through a uPVC frame casually. You will hit the steel reinforcement or, worse, the drainage channels. Fix through the outer flange or use the batten method.
Keeping the weather out
A board keeps out the rain that hits it and lets in everything that runs down the wall above.
- Tape or seal the top edge, and lap any covering so water sheds outwards and downwards.
- A bead of sealant or a strip of duct tape along the top and sides makes a large difference to a driven rain.
- Do not seal the bottom edge completely. Anything that gets behind needs to drain out rather than pool against the frame.
- Expect condensation on the inside of a boarded opening, because you have created a cold surface with no ventilation. See damp and mould if the board is staying up for more than a week or two.
A door rather than a window
A broken external door is more urgent than a window and slightly different.
- Secure the opening first, even crudely. A sheet of ply screwed across the frame beats a door that will not latch.
- If the door is intact and only the lock has gone, screwing a batten across the inside of the frame at two points holds it far better than the lock did.
- If the frame itself has split, the fix is a long batten spanning well past the damage into sound timber on both sides.
- Keep one usable exit. Boarding every door is how a household ends up unable to get out in a fire, which is a much worse outcome than the one you were solving for.
See reinforcing a door and frame for the permanent version, which is a different job done calmly rather than at midnight.
Living with a boarded room
The thing nobody plans for is the dark.
A boarded window removes all daylight from that room, permanently, until it is fixed. A room that was pleasant becomes a cupboard, and in a household already short of light and power that has a real cost.
- Board the least useful window if you have a choice about which opening to sacrifice.
- Consider a clear panel. A sheet of polycarbonate, or an offcut of twin-wall roofing sheet, gives you daylight and reasonable security, and is worth keeping in the shed for exactly this.
- Plan the ventilation. A boarded room with people in it needs air from somewhere, and if the window was the ventilation you have just removed it. Leave a door ajar, or drill a few holes high and low in the board and cover them against rain.
- Write it on the list. A board is temporary. Every week it stays up it becomes more permanent, and boarded windows are also a visible signal that a property is empty or damaged.