Worth insulating?

pledgeX

We have a timber framed house. We're soon going to rip out the plasterboard in the kitchen. Whilst ripping the plasterboard out I was wondering if it would be worth installing some celotex style insulation between the studs.

The query I have is whether this will be worth it. It's about 6 metres worth of external walls that I'd be insulating, but the rest of the house will be untouched.

Will insulating a single room help, or will the warm air just go to another room in the house and escape that way?

TheCyclingProgrammer

Insulating could be good if done right but I'm afraid you can't just stick a load of celotex in there without properly considering the effects of interstitial condensation. The wall has to be correctly designed as IC could destroy your building long term.

There isn't one single approach to this and I recommend the green building forums as a starting point.

Our house is mostly brick cavity wall but the front of our bedroom that overhangs the downstairs bay window is a timber frame, with render outside and the inside was lath and plaster in a bad state of repair. We ripped all this out and took the opportunity to insulate this timber section and it has made a difference but again a lot of consideration was needed. The outside sheathing and render had to be assumed as non-breathable therefore we had to ensure we left a ventilated cavity behind the insulation to allow any moisture to escape (we effectively had a passive ventilation stack with air entering the ground floor brick cavity via air bricks, up into the first floor void and up behind the celotex via small gaps left below floorboard level, up to the loft and put via soffit vents). We also tried to minimise the amount of moisture entering the wall in the first place with a vapour barrier. We fit 50mm between the studs (with 50mm air gap behind), tightly fit, a further 12.5mm inside the studs which helped minimise cold bridging somewhat, taped all the joins, sealed around the perimeters of windows then added a polythene vapour barrier for good measure sealed with butyl tape before plasterboarding and skimming.

That should give you an idea of some of the challenges involved. The room stays warm, the only downside is due to the walls being much warmer and water vapour in the air condenses on the next coldest spot in the room - the window. We get lots of it unless we leave one window cracked slightly overnight (fortunately our wooden shutters minimise the draft). The humidity isn't especially high in their either but the double glazing is about 15 years old and gets very cold and we really ought to getting a newer more efficient low-e sealed unit.