Wall type for External Insulation

Block on flat and external insulation. No cold bridging at the junction between new and old.

Just wondering, if it's ok to do external insulation on the mass concrete structure then why do you think it's not ok for block on flat. As for drylining a new build ???

Some straight shooting there from Mr Eastwood.

So back to the OP's concern. They have "solid concrete" walls in an older house which they intend on applying EWI to, but want to know how a future extension should be constructed to function best with the EWI. C. Eastwood recommended a double-leaf with 140mm cavity of which 100m should be PIR and then 30mm insulated plasterboard internally.

My question is: If the OP is going for EWI anyway, why not have a standard cavity at 100mm, but fully filled and then EWI on top of this? That eliminates the gaping cavity, insulated plasterboard, increases the internal floor-space and the cavity is afforded the protection of the EWI. Or do you foresee many defective EWI's going bad and leaking to the point where even a fully-filled cavity will be problematic?

If you have been given biased advice that the 225 mm thick solid block wall is the “best way to go”, that is correct only for the mason/ builder. He will still get his €2.00 per block and finish the wall in 1/4 of the time it takes to construct an Insulated Wall.

It is not me who is constructing anything. I was just replying to the original query.

Seen someone recently building their kitchen extension with quinn lite style blocks ( or what ever they're called ) , solid block wall and external insulation .. looked like a decent job -

Would some thought want to be given to the use of the small extension and how it joins the rest of the house , and wether extra thermal mass is a good thing ?

If your building a kitchen or living room that opens directly into a living space in the existing house it might make sense to have a wall that works the "same way", ie plenty of insulated thermal mass to "hold" the heat same as the existing house -

A Passive-house foundations and ground floors are all constructed on hi-density insulation.

We were discussing an old house and proposed small extension not passive house construction

The only reason that a 225 mm conc block on flat is constructed in a dwellinghouse is to support an overhead load like a precast reinforced concrete floor.

Kieran. dande67 asked for advice on external Insulation on an old solid concrete wall house, and also about constructing a small extension.

Solid concrete walls are very old walls and most do not have DPC’s.

I therefore gave dande67 some very simple practical advice for the 2 problems given

I could of course have given a person with little knowledge of present day construction (based on the questions asked) instructions to download all of the Technical Guidance Documents and inform them why there are many versions of each TGD and explained why and also inform them that the grey areas on the TGD are the Building Regulations, instructed them to read all of the TGD’s, and get Homebonds House Building Manual etc and read and comply with everything

I could have given all the relevant sections OR given advice to construct a 225mm Cavity Block Wall. But no, I gave very simple practical understandable advice

As you have prima facie done - I could also have explained that you do not have to comply with the TGD’s (why would anyone bother) when you can do something different that’s equivalent or better to that as specified in the TGD and that you would be PRIMA FACIE in compliance.

But I prefer to leave all the Technical Stuff, than many builders don’t understand to Experts like yourself.

I love the part where you quoted the following:- "C4 - The floors, walls and roof of a building shall be so designed and constructed as to prevent the passage of moisture to the inside of the building or damage to the fabric of the building"💧💦💦☔️ 😂😂😂😂😂😂😂😂😂😂😂 it’s a pity that this doesn’t happen on All of the present construction jobs.

You also state:- “Once your EWI system is suitable to prevent the passage of water you do not have a Build Regs issue.” NOTE- You forget to warn Readers that the suitable EWI system MUST be done by Competent People or the Building Regulations won’t prevent the passage of rainwater through the wall.

I do not know if you have ever seen the damage in a dwellinghouse where a €24,000 EWI was carrier our by incompetent morans, plus the mental stress that it causes to the Homeowners

You also state:- “The technical guidance documents if followed are a prima face way of ensuring compliance with building regulations but that is not the only route to ensure compliance.” NOTE:- Many builders and most of the tradespersons working on building projects have never seen any of the TGD’s not to mind different methods of compliance.

I should have told dande67 all your advice the first instance, and it would have instantly solved all his problems.

Thanks for all your advice Kieran, I will pass it on to Bob the Builder.

@C. Eastwood it is better to give no advice than free advice that is wrong.

At least the person you took your name from only played the role of a cowboy.

The most used method of constructing walls to attach external insulation to is 9" cavity blocks.

This is what is currently being used on new build sites in the Dublin area.

After that there is either an acrylic render or a brick slip or stone slip attached to the insulation to finish it.

The OP suggested to build a 225mm wide wall block on flat and not cavity wall. A solid block on flat wall is structurally far superior to a 225 cavity block wall.

You also stated "A New build dwelling must be in compliance with the Building Regulations. It must have a cavity wall. With insulation in the cavity or insulation in the timber frame inner leaf." I quoted the relevant section of the Building Regs to show that this statement was indeed incorrect, there is not such assertion in the Building Regulations

No matter what wall system the OP has choosen all components should be install by suitable skilled trades men. If he has employed suitably experienced professional to design, tender and inspect the works "morons" should not make there way on to his site.

The OP has said that he is applying EWI to the external face of their existing home therefore from a thermal bridge and watertightness continiuty view point a solid 225mm block on flat wall with EWI system would be the best solution in my opinion. While I note your issues with water ingress on a EWI system I have personally designed and signed off on many successful newbuilds and extension with a 225mm solid wall and EWI. Like any project the key is to get the design right first then to make sure it is excuted correctly on site but this goes for all build methods!