EWI - Is Drylining irrelevant?

ayeboy

I have a guy lined up to externally insulate solid 300mm thick walls with 100mm PIR. We were just chatting and I mentioned that I also plan to dryline the walls (approx 42.5mm thick). He said this would be a waste of time as it negates the benefits of EWI - i.e. walls acting as a thermal store.

Is he correct in this or would adding drylining benefit property even more?

Can't go any thicker than 100mm ewi as it is a retrofit job and soffit space wont allow.

Thanks

BryanF

ayeboy wrote: »

I have a guy lined up to externally insulate solid 300mm thick walls with 100mm PIR. We were just chatting and I mentioned that I also plan to dryline the walls (approx 42.5mm thick). He said this would be a waste of time as it negates the benefits of EWI - i.e. walls acting as a thermal store.

Is he correct in this or would adding drylining benefit property even more?

Can't go any thicker than 100mm ewi as it is a retrofit job and soffit space wont allow.

Thanks

interesting conundrum.. its not a wast of time from a U-value perspective, most of the easier to use software's would confirm this, and it would be hard to calculate the lost thermal store value. BUT like most things with building maybe there's another way of looking at this.
you mentioned the soffit depth being an issue, you do understand that a good ewi ciontractor should remove the soffit and fit the insulation to meet the attic/roof insulation? if you were to get a roofer out and complete the ewi to attic ins by filleting the roof and extending the eaves slightly, how much would that be V dry-lining the whole house + the inconvenience and re decorating
do consider the windows/ floor / penetrations details and PROPER vents when when doing the EWI. you only want it done once:)

sydthebeat

while i wouldnt say 'waste of time' i would say its counter-productive.

insulation works best when it all occurs on one plane. Having two layers of insulation (100 + 30) 300mm apart is not a preferrable situation. As brian says above, you would be much better off trying to get another, say, 50mm to the EWI. It would cost you a fraction of what it would cost to dryline internally. There are some remedial measures to be taken externally but these are not major.

You also get the advantage of:
1. more space internally
2. very little chance of condensation issues (once vented correctly)
3. much better thermal storage

sinnerboy

Put the €€€'s you are prepared to spend on IWI into the proper detailing of the EWI.

- extend the EWI down to top of footings ( yes - dig up your footpaths )
- move the windows out so they line up with the EWI layer
- cut the existing external cills away
- remove gutters and facias and ensure the EWI links ups with the roof insulation

Any "nominal" U Value of a wall can be shot to pieces without attention to such detail. And worse you can get localised condensation - one gets an increased risk of this with higher nominal U Values .

A thermal bridge works like putting your thumb over the garden hose - just like as you increase the water pressure with the hose - heat flows with greater intensity at thermal bridges.

In short simply dry lining without attention to detail could see you harvest some of the black stuff.

And I don't mean Guiness.

ayeboy

Thanks for replies lads. Already had old windows taking out and and new cills placed 100mm out to accomodate ewi. He also suggested digging down a bit below ground level so I'll dig down to the footings.

Good points regarding linking up with attic insulation...something I hadn't thought about and will need to discuss with him!! Cheers