How to insulate timber extension?

PhGage

My Mother in Law has an extension which is clad in timber, some of which is buckled and is now in need of repair on all 3 sides.

The extension is wretchedly cold during the Winter. Having looked underneath the timber, it's just a basic timber frame with plasterboard in the kitchen, some rockwool insulation between the struts and in the voids of the frame and then the shiplap cladding.

Planning restrictions mean that she has to retain the timber cladding so we can't replace it with Kingspan External Wall Board and rendering. We'd like to upgrade the insulation but aren't sure whether putting in something like Kingspan (?) insulation boards means that we'd also need to install a breathable membrane between that and the external timber cladding or it and the plasterboard.

I'd be grateful for some advice.

cyclonebri1

How thick is the wall??
Can it be enlarged either internally or externally, (as you are going to open all sides), by adding extra timber to increase the wall thickness?

Kingspan or celotex is the material and should have been speced and fitted in the 1st place in my view.

Regarding ventiation, if it were me, say the stud work was 50mm wide, I would tag onto the out side some 90mm timber.
The insulation would fit up to that from the inside and it would create an air gap under the cladding. You would need inlet and outlet at the top and bottom.

I my view you do need a vapour barrier to the inside, foil backed plaster board should do the trick.

My view isn't backed by any professional status by the way, but I'm a pretty good jack of all trades:D;)

PhGage

It's standard plasterboard on a 50mmx25mm timber frame with the cladding, so, probably 75mm deep at most. Planning restrictions mean that the external footprint of the extension can't be increased (it's about 2.4m x 2.5m). The extension was built around 28 years ago and apparently didn't have any insulation at all until she had the kitchen plastered 15 years ago when the plasterboard and insulation were put in.

The internals of the extension are very badly thought out. Adding to the frame internally would involve digging up the floor to move a radiator as well as moving some of the plumbing (sink, dishwasher, washing machine).

I think fixing this extension may well require an extensive revision to the budget. :eek:

Thank you.

cyclonebri1

PhGage wrote: »

It's standard plasterboard on a 50mmx25mm timber frame with the cladding, so, probably 75mm deep at most. Planning restrictions mean that the external footprint of the extension can't be increased (it's about 2.4m x 2.5m). The extension was built around 28 years ago and apparently didn't have any insulation at all until she had the kitchen plastered 15 years ago when the plasterboard and insulation were put in.

The internals of the extension are very badly thought out. Adding to the frame internally would involve digging up the floor to move a radiator as well as moving some of the plumbing (sink, dishwasher, washing machine).

I think fixing this extension may well require an extensive revision to the budget. :eek:

Thank you.

I don't think it will be expensive in terms of materials, but from what you say it's the reorganisation and the labour entailed that fix the figure.

I shouldn't say this but do you think sneaking an extra 50mm all round will devastate the planet???, I'm sure you know what I'm saying?;);)

muckybutt

I personally would go for actis insulation, I used it a few years back on a refub job.

Excellent stuff to work with and far better insulation values than kingspan. Building inspector was dubious to begin with until I showed him the tech spec of the stuff.

All you would need to do is take the plasterboard off, tack the actis to the stud work, tape the seams up with foil tape giving you a vapor barrier, then plasterboard on top.

PhGage

cyclonebri1 wrote: »

do you think sneaking an extra 50mm all round will devastate the planet;)

I may need to make some very careful measurements.

I personally would go for actis insulation, I used it a few years back on a refub job.

Thank you for the link, I hadn't seen that before. We have solid rather than cavity walls in our own home and most of the recommendations to improve our insulation are so bulky and expensive that I hadn't looked at the issue recently but Actis looks very promising even for us.