Hi everyone

I'm currently planning a energy-efficient refurbishment of our seventies house, a project about which I have a boat load of questions. I'm going to have to get a lot of the work done, as I have no DIY experience. I'm currently selecting builders/plasterers etc and none of them have previous experience at working to very demanding airtightness and insulation criteria.

I'm rapidly catching up by reading around (this forum, navitron, haynes insulation manual, rest of the internet) but I've got a couple (well three currently) questions that I cant seem to get clear answers to in this way.

As I'm going to need to discuss this project meaningfully with these tradesmen it would be a great help to me if you could give me some advice please on the following questions:

1) Insulating external walls internally using PIR boards. I'm concious of creating a thermal envelope.
- what happens when I get to ground floor ceiling/first floor floor level. I think I remove ceiling and take insulation up. Is this correct? Or do I pull up the floor and take insulation down, or a combination? Theres lots of info about insulating just a wall but very little detail about dealing with this aspect.

2) The house is unfilled cavity construction. At the joist ends I insulate around and then tape/seal to make sure that water vapour cannot get from inside the house to the joist ends, is this correct? I'm thinking that is what this picture shows: http://www.navitron.org.uk/forum/index.php/topic,11089.msg121478.html#msg121478

3) First floor ceiling level, I have a traditional breathing loft with good-ish (270mm) insulation. Do I need to add a vapour control layer at the first floor ceiling level?

Many thanks

Thank you very much Nick. Sounds straight forward enough, in theory that is.

The cavity interestingly isn't ventilated, there's definitely a cavity and definitely no airbricks anywhere, but I'll follow the advice as above.

More questions soon, especially when we get to hands on stage

Hi DJH, thanks for the reply.

<blockquote>Firstly, why are you not filling the cavity? Come to that, why are you not using EWI instead of IWI?</blockquote>

I dont trust blown cavity wall insulation full stop. I cant use EWI as it is a link-detached house and so I cant insulate externally, The reason being that one side of our house is effectively the border with my neighbours drive and if we were to insulate and render externally this would intrude on their property by the width of the insulation and render. So whilst this would have been a good choice it wont work. I could I suppose render three of the four walls but that would look odd, plus I'd probably also need planning permission.

<blockquote>Note that what you're doing by taping is slowing water down, not stopping it. Water vapour will migrate through the joists. So you need to be sure that where it ends up - in the cavity - either it can evaporate away and out, or that the cavity is warm enough that the water won't condense. Wood isn't even airtight along its length, BTW, mainly because of cracking.</blockquote>

OK but I guess then I am doing my best to limit moisture. From the above answer by Nick I do this by sealing at the joist end, insulating with PIR, having a VCL and taping.

<blockquote>Are you adding more loft insulation? It sounds like that would be a good idea. What you do need to do is make the ceiling airtight, so seal it up especially where electrics or plumbing go through the ceiling.</blockquote>

Wasnt actually intending to add more insulation up in the loft, I thought I'd reached the point of diminishing returns


<blockquote>(No air brick)That doesn't sound right to me for a 1970s build, though I'm not an expert. Where is it?</blockquote>

It is odd, but there is definitely 100% no airbrick. And there is definitely a cavity.