Door threshold and cavity wall.

craiginuk · 4 Sep 2010

I am hoping someone can help. We are about to have oak flooring put down in a dining room which is part of a ground floor extension completed in 2002. (before we bought the house)

There is a door threshold where the door meets the cavity wall. This has been a bit loose to stand on for the past few months. I lifted it this morning with a view to removing for the new oak floor to run right up to the door.

//www.diynot.com/network/craiginuk/albums/6431

See pictures. It does not seem right. There is nothing supporting the threshold where it meets the upvc door. It is just resting on the row of bricks. If that makes sense.

My question(s). How can I support the new oak floor and how do I insulate this area. The room ahs always been very cold.
Do i need to refit the threshold? If so, how do I fasten it. It was just glued down to a membrane before which does not seem right.

Thanks

Craig

r896neo · 4 Sep 2010

that was obviously at some point converted from a window into patio doors. Your solution would be to get some DPM and line the cavity to create a trough. Then fill this trough with concrete to finish flush with the floor inside.

If you are concerned about cold bridging you could create the polythene trough and wedge a piece of insulation against the outside leaf of the cavity and then fill in the remaning space with concrete but full filling with concrete will give a better result.

craiginuk · 4 Sep 2010

Thanks - don't think it was a window before (it's in the new part of the house) but maybe they read the drawing wrong when they did the extension and thought it was a window. Then made a bodge to fit the door.

Is it quite normal to fill the cavity with concrete below a door?

So I just line the trough with some DPM and then pour in some concrete. How long roughly will it take to go off? Floor is going down Wednesday week after next.

r896neo · 4 Sep 2010

this would be the normal way i would do it if faced with your situation but others may have their own recipie if they want to chip in.

Normally on a purpose built door opening the inner leaf is dropped down and dpm run out to the back of the outer leaf and the concrete floor would have been poured right up to the face of the outer leaf.

craiginuk · 4 Sep 2010

Thanks - sorry about all the questions. Do i need to allow for contraction/expansion when i pour this small amount of concret? or do i just go to the same level of the floor in one go?

r896neo · 4 Sep 2010

no just all in one hit will be fine.

Ideally you would let it dry out for a few weeks before doing your wood flooring but it is such a small quantity it shouldn't really matter.

If you are concerned you could simply lay a bit of polythene over it before you lay your wood.

Just to confirm, when i say trough i mean folded up at the sides as well to form a complete envelope around the concrete, but i guessed you probably understood that.

craiginuk · 4 Sep 2010

Yes - thanks - understood that about the trough. Have bought some DPM as well as some joining tape so will make a proper compartment for it.

Could I end up with condensation on inside if the cavity wall is bridged or is it ok because it's under floor level? Sorry - all very new to me

r896neo · 4 Sep 2010

It technically will be a cold bridge but in reality it won't be a problem.

If you are concerned you can as i mentioned earlier put a strip of insulation against the outside wall as this is effectively how reveals are closed at the sides. But in reality i can't imagine it being an issue.

craiginuk · 4 Sep 2010

Thanks for all the help! Could you point me in the right direction for a strip of insulation. Will wickes do it? Cavity is only 70mm across so how thick should the insulation be?

Also is there any advantage in using a double layer of DPM as I bought loads of the stuff.

r896neo · 5 Sep 2010

frankly any rigid polysterene will do, even a bit of old packaging that is straight and not too thick. For the best result a bit of celotex or similar rigid pir insulation.

You can buy purpose made reveal strips so ask if they have those but probably only something you would get in the builders merchant and you might have to buy a bundle of 50.

Seeing as it's only a 70mm cavity try to get the thinnest you can. i.e.25mm or so.

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Door threshold and cavity wall.

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