Cavity Querie

[staningrimsby]

Hi Guys,

In the process of building my extension in which will hopefully sit a pair of external upvc french doors. The extension has a 90mm cavity all round, my question really is were abouts should the doors sit in relation to the opening (i.e. on the inner skin, outer skin or over the cavity).

if it is on the outer skin for arguments sake what do i do about covering the cavity especially in the floor ???

Cheers in advance
Stan.

 

[noseall]

ideally the door should sit partially (10-15mm)into the closed cavity, as to absolutely prevent any seepage of damp from the outer leaf.

most fitters fit the internal edge of the jamb flush with the inside edge of the outer course.

cavity closers are proprietary items sold to suit regular cavity sizes.

we use screed at floor level. cut through the dpc, remove the top course of bricks, lay the dpc back down, lay some dpm into the trough and then lay the floor screed up to the door sill.

its a bit of a bu**er if your course of masonry just below dpc is blocks.
you then have to hack at it with a bolster chisel.

 

[Shytalkz]

Nose, I think it's 30mm now, for Part L requirements.

 

[staningrimsby]

What sort of cavity closures am i looking at Nose, is there anything in particular i should be looking for ???

 

[noseall]

thermabate

here is another...

any b.s. approved or licensed proprietary brand will do.

 

[staningrimsby]

Cheers for that Nose, what exactly is it then it looks like a piece of insulation stuck onto some form of more rigid material ?

 

[noseall]

yeah, basically they are dense styrofoam blocks or strips with dpc bonded to them.

some have specific fixing tags bonded to them also.

they cost a lot and are in my opinion (and woody's) a bit of a rip off.

they do solve the problem though.

 

[staningrimsby]

Cheers for that Nose i will nip to the builders yard as soon as me roof windows have arrived, i might need to come back to you later though for a more in depth discussion into that floor cavity tho...

 

[staningrimsby]

we use screed at floor level. cut through the dpc, remove the top course of bricks, lay the dpc back down, lay some dpm into the trough and then lay the floor screed up to the door sill.

Noseall, had a brainwave today, it still blooming hurts.

Would it suffice if a made a concrete step 1200mm long by 300mm wide and approx 20mm thick with reinforcing bars in to cover both courses and the cavity in the floor obviously sat on DPC, then my french doors could sit on this ???

 

[noseall]

i can envisage two problems with this:

1. there is a high risk of damp transmission from direct external exposure.

2. thresholds on upvc doors are already quite tall, this system will only make matters worse.

if you understood me correctly, you will realise i was referring to removing the internal top course of bricks as to allow for screed thickness.

 

[staningrimsby]

if you understood me correctly, you will realise i was referring to removing the internal top course of bricks as to allow for screed thickness.

Yeh i did understand what you were saying reference that but what actually stops the concrete screed going into the cavity ?? am i just relying on the DPM to hold the screed ???

 

[noseall]

Yeh i did understand what you were saying reference that but what actually stops the concrete screed going into the cavity ?? am i just relying on the DPM to hold the screed ???

yes.

form a trough using the dpm. pinch and dog ear the corners to make a kind of parcel.

the dpc will be filled with lean mix concrete up to within 3 courses of the dpc anyhow. at the door junction this could be filled up to the underside of the flooring concrete.