House man

The building is already going to be undergo a K rend, which would stop any air leaks and could help a bit with thermal bridging? If you are going for K rend to seal all the outside, wouldnt IWI be better then in this case?

Ive been back and forth about this but wanted more answers on this matter Considering your property needs work outside and your going for a full reno, why would you choose EWI over IWI? This is where im confused Your source of heat are the radiators, so if you go for EWI, your radiators are first heating your inner block, then your cavity void with some wall ties, then your outer block, and then the heat is trapped in by the EWI, But with IWI, you are not heating up the inner block, cavity and outer block for free as you are trapping the heat almost directly from the source which is your foil backed PIR boards attached to your inner block. Plus you would have air bricks or weep vents in your cavity that brings air in, a hole in your armour when it comes to ventilation. Would you not do IWI over EWI?

Thanks for the reply, Wondered if you lose any heat through the framing battens?

Thank you for your response I would have thought theres a point at which if you added any further insulation it would not help. Ive done a new extension and added 50mm in the cavity with air gap. However i dont believe any cavity job can be complete due to all those wall times that go in, hence the IWI One other thing about IWI is that are you not losing heat through the battens between the PIR insulation?

The room is 4.3m x 3.6m The rest of the home is large enough to put 50mm PIR boards for IWI but was thinking if it is advisable to go for 25mm to not make the room too small? Thoughts? Cheers

Starting to work on the inside of the house now and deciding on which one is better to use for insulation boards or mineral wool? Any experience and input would be greatly appreciated

Got space for tank in garage, is it complex to connect up the pump to the existing house? 200sqm home and 3 bathrooms, what kw and which brand pump you recommend? And more importantly to anyone that does have one, are you even saving? considering im looking at maybe 10k

Im saying I suspect the builders have not correctly installed the boards edge to edge and left gaps which were not filled, and am just wondering exploring further insulation options. It is a new extension currently ongoing. That makes sense, at least we find our warm air gap in the inch. Can you state how much state how much of a difference the 50mm internally had?

It is possible but why not put the 50mm PIR between the battens and plasterboard screw straight infront of it saving the 25mm?

Having read the latest comments i assume the best action would be to have 50mm of insulation inside behind the plasterboard rather than 100mm on the outside, especially since im suspecting the builders of not taking the care to thoroughly execute the installation of the 50mm boards without gaps around the dozens and dozens of wall ties. The silicone K rend alone should probably more than suffice for providing the additional protection to reduce bridging and condensation. Now would 50mm rockwool or 50mm celotex be the best option between the 50mm battens behind the plasterboard? Any better alternatives?

Very interesting. I find it surprising that adding 100mm on the outside equals an absolute zero advantage in terms of U-value. And that the 50mm gap is the equivalent to an infinite gap if you know what I mean. Any disadvantages with a complete cavity fill with 50mm inside and 100mm outside? Anything im missing? Except not paying proper attention and getting it right the first time?

Thank you, was more the answer I was looking for in the beginning but got a lot of insight from nod, now so I have made my mind up to go ahead with the 100mm XPS under the render, but would like to ask if I should fill that cavity at all? The roof isn't on yet so wondered if you would think of giving it a fill of some sort of leave it as it?

Hi Nod thanks for your input, what I really am trying to comprehend is the the effectiveness of the EWI while there's a ventillation gap. If the air gap would mean the outside 100mm EWI has its heat saving properties reduced due to the 50mm gap in the cavity.

Hi guys, Ongoing extension Have 50mm cavity insulation with 50mm air gap, suspect 50mm insulation boards not fitted properly Just thinking wouldn't it be kind of useless to have 100m external insulation wall insulation since I have a 50mm air gap between walls? Thoughts?

Hi guys, not gonna lie i am grateful and very moved by the amount of comments and time to try help me out. I was under the impression that having there a space would be ideal incase of any leaks or if I want to make some small basement area in the future or even just a small underground storage. After reading these comments and speaking to some builder friends I've been advised that the odds of solid tested copper work leaking water is next to zero and although space would be ideal if it was there, there's no use taking out tonnes of soil at extra cost, and the house is not very wide so any digging under could cause a foundation structural issue. And to answer peterW, im using joists and floorboards to match existing house and the inspector said we ideally want an airbrick every 2m