How to insulate and damp proof a solid wall?

[iturner1]

Hi,

I am in the middle of some building work to join an exisitng brick outhouse with my house.... I'm not sure of the proper terminology here... the walls to the outhouse are 2 layers of brick with no cavity. Approx. 200mm thick.

I've had some plans drawn up... and have been given the following instructions on how to damp proof and insulate... "wall lined with 1200mm gauge visqueen dpm 75mm styrofoam polystyrene wall insulation and 12mm plasterboard finish."

What I was planning on doing is screwing 3x2 battens to the wall, with visqueen behind them. Then filling the space between the battens with insulation (standard rockwool 75mm insulation) then cladding the front of the battens with 12mm plywood and 12mm plasterboard.

I know I want to put a number of services through the wall - outside tap, various soil/drain outliets and electrical socket.

What concerns me is what about all the holes in the visqueen? There are going to be a number screw holes from battening and some additional ones wherever I've pushed pipes or cables through the wall. Is this a problem? Should I be doing something to seal the holes?

any help much appreciated,

cheers

Ian

opinions most welcome?

 

[JohnD]

on a different tack...

If the room is going to be warm, and the wall damp, you will get interstital (?sp?) condensation forming within an open insulation material like glass fibre. And once formed the wet will not be able to get out, it will just accumulate behind your impervious lining. A closed-cell foam insulation (such as glass foam) prevents this which may be why your spec says styrofoam (which I understand to be the American trade name for expanded polystyrene).

I would also be inclined to use a moisture-proof vapour barrier like foil-backed plasterboard on the room side. The battens will want drenching in cuprinol green if they are wooden (or you could presumably use metal). I don't know if or how the void should be ventilated. What does your specification say?

 

[iturner1]

The room willl be warm.. its actually going to be partitioned into two rooms, one containing a shower, sink and toilet. The other is a utility room containing a hot water cylinder, boiler, washing machine and dryer. As its warm it'll probably also be used as a drying room for clothes.

I like the idea of treating the timber, my local builders merchant can supply treated timber as I've used that before for a decking project - I seem to recall it being called CCA treatment? Is that the same stuff?

Do I need to worry about the holes in the visqueen, e.g. from the waste pipes, ventililation trunkung and screws holding the battens to the wall? Or am I being too paranoid.

The ventiliation recommended in the spec is a bit confusing as I think its just boiler plate text, to quote it:

"Provide and fix Vent Axia Centrif humidity controlled extract fans in kitchen rate 60l/s.
Provide and fix Vent Axia Solo timer timer controlled extract fan in Ensuite and Bathroom 15l/s with 15min overrun"

I've heard concerns about humidity controlled fans and their cost/life expectancy.

In these two rooms I assume I'll need to fit two extractor fans? The shower room presumably as described above, but what about the utility - its not really a kitchen?

thanks for the help

 

[andymarshal]

hi mate, what i did in your situation is fixed tanalised roofers lathe to the wall, this enabled me to straighten it up and then i screwed foil back boards to the slate lath, it worked really well

Cheers

 

[Swiss Tony]

The Visqueen is to prevent the condensation. I really wouldn't worry about the holes you make in it. Its not as if it is going to be swamped with water.

Unless you need to comply with Building regs I probably wouldn't bother with the ventaxia in the Utility as it is unlikely to get steamed up like the shower or kitchen. If you are working to Building regs then ask the Building Control Officer if he thinks you really need one. I guess not.

Having fixed the visqueen, battens and wedged insulation between, why are you adding the plywood AND plasterboard? Plasterboard would do the job on its own.