Celotex-Cavity or not?

[Swimbikerun]

We are about to renovate a large Victorian property and want to insulate internally. Celotex has been recommended by a couple of friends, who have put in on walls on top of wooden batons to create a cavity. A builder we are in discussions with has suggested just attaching it to the wall without a cavity. Does anyone have an opinion on this? It's going to be very expensive and I really want in to make the house warmer... Thanks

[tricot39]

Read this recent thread:
www.mumsnet.com/Talk/property/1593833-secondary-insulation-victorian-terrace

We installed some without a cavity before the manufacturer's settled on their technical advice. I now worry about it. If your builder is suggesting no cavity i would suggest you take any advice he gives with extreme caution.

[Swimbikerun]

Thanks for the link. Have you had problems with your insulation tricot? It's hard to make decisions on things when there are so many different options. The house has 30 year old PVC windows, and we are hoping that replacing the glazing will help with heat retention.

[tricot39]

No problems as yet - but it would be years before they became apparent. Read the conference proceedings and dont do anything until you have a firm grasp of the technical issues.

[EdgarAllanPond]

i think there was a good post by Piglet John on this subject, someone was asking about a nice old property....

Victorians had heavy furnishings instead of insulation...

[Swimbikerun]

Looking at other threads and reading the conference proceedings. Thanks for the pointers. Looks like I need to think whether we should actually be putting up internal insulation at all. I wish there was a definitive answer. I really don't want to end up with damp problems. Friends who have insulated have said their house is so much warmer, I just assumed it was the way forwards. We might be saving thousands of pounds if we don't do it.

[PigletJohn]

I haven't heard about the gap problem. I presume it is to do with condensation. Drylining should always be done with a vapour barrier such as foil-backed board.

Have a look at the Kingspan site which is very good in specifying applications and installation techniques. I have seen solid walls insulated in Switzerland, either internally in old houses, or externally in new ones, with rigid foamed slabs, so I presume there must be a way to do it properly.

[tricot39]

I followed the kingspan guidance. Shame it was contradicted (at the time) by celotex's advice which in hindsight was most sensible - create a cavity between the existing wall and the insulation. But when you start thinking about unventilated cavities, dew points and interstitial condensation you can lose a bit of sleep.

I think that conference's conclusion that superinsulation of existing properties is unwise is probably right and at the forefront of current thinking. I would pay more heed to that than the insulation salesmen.

[Swimbikerun]

Have been doing a lot of research the last couple of days. We are now worried that by doing the internal insulation we are going to end up with a whole lot of other problems. Now thinking we might put in 2 wood burning stoves and be prepared to put the heating up a bit. House needs re plumbing so will have new central heating system. Wonder if it's worth putting 2 radiators in any of the rooms. Thanks so much for spending the time to reply to my post.

[PigletJohn]

If you're having a nw condensing boiler fitted, which is most efficient running at 60C, IMO it's a good idea to have rads 50% or more bigger than teh calculator shows you need.

I find the calculatore is a bit underpowered because it gives the power needed to maintain the room at temp on an averagely cold day. If you want tro heat iit fas from cold, or if the weather is unusually cold, you need more power.

If you have TRVs then there is no risk of any room being overheated.

I'm very keen on insulation and am not familar with the problems you mention. Drywall insulation or external slabs are uncommon in the UK because they are fairly expensive, but are very popular in the (very cold) Alps, even in new-build. I think they look fine if the house is rendered or tile-hung over the slabs.

[tricot39]

Hi. Thanks for the update. There are of course lots of other things you can do to reduce heat loss. The est website is really good and has a refurbishment guide for download. Good luck!