Leaking aluminium bifold doors

3 Feb 2023
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United Kingdom
Hi there,

I’ve had an outbuilding built at the end of garden with bifold doors. Initially it was built on a single foundation slab of insulated reinforced concrete. All was well in the summer aside from the odd bit of mould due to infrequent use but in the winter months when the rain came I noticed that the laminate floor inside became a bit squidgy to step on. It seems water was coming in from the bifolds or from the 1m depth patio step outside.

The builders had done a runner and weren’t answering my calls, so I got two sets of separate builders and window/bifold installers to come and take a look. The builders said that the step outside the front of the bifolds was too high, and that it was higher than the inside FFL. The bifold fitters said it was the frame and that the bifolds should be reinstalled.

In the end I decided to go with builders in lowering the step so that the bifold sill has a 20mm gap before the top of the patio step.

In that process I noticed two things….first was that the original builders had used ply wood to rest the bifold frame on and because of the leak, the wood had become wet and soggy. Second was that the bifold installers hadn’t used silicone to seal off the ends of the sill. I’ve seen a few videos of installers saying that it’s very important to seal the ends to avoid ingress.

As it stands now, the step outside has been dropped, the 20mm gap underneath has been cemented over with a membrane on top of that (though it’s hard to say if that alone will help).

My question is, will the above do the trick? Or will rainfall onto the bifold itself still somehow find its way into the tracks inside and under the floor? See pics attached

Thanks all


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You could really do with the plywood raking out and mortar putting in.
You might be able to mix up a small amount of mortar and force it in with a finger jointer (tool), keep repeating until you've filled it.
It will be tricky getting the plywood out, as you can't knock it out, from one side to the other.

If left soggy plywood may start to swell the laminate flooring.
Cheers for your help, I agree with you in that it’s impossible to remove the plywood without taking out the bifold frame. The question is, what can I do from the inside under the bifold frame? Could I mortar that too? Would silicone along the entire thing keep the water from seeping under the laminate? At the moment, the current laminate is warped anyway, so the entire floor will need replacing but I’m keen to solve the issue before laying anything new down
One the inside if you can get mortar packed underneath that will replace the plywood. I would stop the mortar say 25mm from the face of the frame, I would them put a strip of celotex or expanding foam (cut neat when finished). This should stop the cold bridging from the cold outside meeting the warmth inside. If you don't stop this, you'll get condensation which will wet the floor again.

You may need to get a bit of anthracite trim to make it look nice, depends on floor height etc.
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Given the state of that install I'd seriously consider removing and reinstalling. If you're set against that, then check the drain works ok and isn't somehow going inside but mortaring seems a must

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