counter battening - to insulate or not

[1john]

I am about to purchase a 1925 property, it is brick built with a cavity which has had cavity wall insulation added. I am planning to hack off the exterior walls and then batten and board them so i can hide various services (pipe work and cables ect). My main thaught is weather or not i should take this opertunity to add some extra insulation in the form of bubble foil insulation. I plan to tack this to the battens and fix plasterboard directly over. My main concern is that I may cause condensation on either side of this bubble foil due to temperature differences. Is this likely and can anyone see any other drawbacks from doing this.

Thanks for reading and thanks in advance for your replies

John

 

[noseall]

I personally can not see bubble foil making an awful lot of difference.

Provided you incorporate a vapour barrier directly behind the boards then you should be ok if using a more suitable insulation i.e. 40mm celotex or kingspan.

 

[1john]

firstly, thanks for your reply, im limited for space and I only thaught of the bubble foil as it is relitavly inexpensive, wont take up much room. i know i may not gain a great deal, my main concern is the formation of condensation as the house is pretty well sealed due to it having cavity wall insulation and there would be no ventilation behind the boards.

Im begining to wonder weather to bother with the foil atall now :S

 

[alittlerespect]

Your best solution would be to run your services and then use plaster dabs to stick an insulated plasterboard to the existing plaster i.e. don't waste your time hacking the plaster off. Not to mention the flat surface that you have to work from - why create problems.

As you already have an insulated cavity around 50mm thickness of PIR insulation with plasterboard will give you quite a good insulation value, if you want to go the extra mile use an 80mm PIR board.

By the time you've messed around with the foil insulation it will be far easier and less time consuming to use the insulated plasterboard. If your not to familiar with plaster dabs you could counter batten the wall with 2.1 tanalised sawn softwood and then screw fix the insulated plasterboard to the battens. whichever you find easiest! Skim coat or tape and joint, decorate and job done!

Regards

 

[Richard C]

Be careful if you’re planning to remove all the plaster from the external walls; if you remove more than 24%, your changing a thermal element (in this case the external walls) & will fall foul of Building Regs. which may require you to bring the whole property up to current insulation standards. You probably won’t get found out unless you’re doing other building work that involves an inspection by your LABC but getting caught can land you with a lot of hassle & a very large bill . It has happened & at least 2 instances of getting caught have been posted on this forum in the last couple of years.

If the original plaster is sound enough to accept dot & dab, I’d leave it well alone & probably go with the insulated plasterboard approach. You can still chase out for new service runs & board over but at least you won’t create any unexpected problems for yourslself. If it's all blown & youve no real option but to remove the lot, make sure no one finds out what your up to!

 

[1john]

thanks people. i cant afford the space of 80mm PU board, i was goint to use 2x1 roofing battens (tanalised) as this doesn't affect the internal space too much also i beleive it's a much better way of getting a straight, flat, true finish. Dot and dab can easily wander about a bit, especially down a long wall. it's a bit messy to be using string lines with ect so i will go for the battens.

I will smuggle small handfulls of the old black mortar in my pockets into the yard when i'm on daily exercise. Although bringing it upto current standards cant be such a bad thing, seeing as the cavity is already insulated (not that i like it) what more can they make me do. i would gladly put min 100mm rockwool or similar between the joists of the ground and first floor and gladly upgrade the lost insulation to 270mm, infact i plan too, also if I was to replace the internal walls upstairs / downstairs then i will rebuild with 4x2 and insulate them with rockwool too (provided they are not structual).

I apreciate i wont make much difference to the u value, really just concerned about the condensation side of things.

 

[Richard C]

When I use it, I don’t have any problems with dot & dab; if the walls are basically flat & true, keep the boards tight & it’s difficult to tell if it’s been plastered or boarded.

also if I was to replace the internal walls upstairs / downstairs then i will rebuild with 4x2 and insulate them with rockwool too (provided they are not structual).

Another little gem to watch out for is that any stud walls between a room containing a w/c & another “habitable room" must be sound insulated (but not the room it serves in the case of an en-suiet). Minimum spec is 25mm mineral wool insulation (I usually use cavity insulation bats) & either 12.5mm “Soundblock” or “Wallboard 10”; ordinary "Wallboard" is not sufficient unless you double up on the boards.

 

[1john]

duly noted about sound, thank you, i thaught 100mm of rockwool may have sufficed although still, does anyone know if i would end up with condensation either side of the bubble foil?

 

[legs-akimbo]

Dot and dab a 38mm or 50mm thermal plasterboard and then mechanical fix with mushroom plugs, you will gain the benefits of the air cavity behind the board from the dabs, you gain nothing more from the air cavity from using stud, the only benefit being you can add additional quilt insulation between the stud. Battening out is sledgehammer to crack a nut territory.
Interstitial condensation will not be an issue as you have cavity walls, this problem only ever arises in solid walls to varying degrees dependant on the fabric.
As for the hacking off of the internal render, there is such a minimil u value here in external or internal plaster surfaces that it is not even taken into consideration when calculating the performance of a wall elements overall u value, it is miniscule so if you hack it off or not wont make a blind bit of difference thermally, but a lot of hard work for nothing.

 

[legs-akimbo]

for bubble foil to work with any degree of effect it needs to have minimal contact... for example if you had it flat against a wall with a plasterboard against it it would be next to useless if its used on a pitched ceiling it needs an air gap at the back and counter battening for air gap before plasterboarding, this is how it works, anything else reduces its effectiveness to virtually nothing.

 

[Richard C]

As for the hacking off of the internal render, there is such a minimil u value here in external or internal plaster surfaces that it is not even taken into consideration when calculating the performance of a wall elements overall u value, it is miniscule so if you hack it off or not wont make a blind bit of difference thermally

You may be right; but under UK Building Regs, if you remove more than 24% & get found out, LABC can force you to upgrade the walls to the latest thermal standards, not just what they were originally; it also applies to external render. People are replacing plaster/render all the time, it’s all rather stupid IMO & very few know about it, probably the only people that do are the ones that get caught out; the trick is not to get caught!

but a lot of hard work for nothing.

Totally agree, as long as the original render/plaster hasn’t blown.