External wall insulation

Jcanty85 · 29-03-2019 11:03am #1

Hi all,

Just wondering if anyone had any thoughts on this. We are planning a new self build (3000sq ft, 2 storey with hollow core slab, large south facing windows with limited northern glazing). I'm currently leaning towards external wall insulation due to removal of all cold bridges and the ability to not have to watch blocklayers constantly. However the site we have is quite hilly so the chance of driving rain is a worry. Instead of building a block on flat internally I was thinking of building a narrow, uninsulated cavity wall (50mm cavity) and then having ewi on the outside. I was thinking of this as it would give me the benefits of ewi, I would still have the "security" of a cavity from a moisture ingress PoV, it would take less blocks than block on flat and I would still have the ability to allow the hollowcore slab to sit on both leafs (with appropriate dpc).

Id appreciate if anyone could offer any opinions on this, pros/cons as all advice is greatly received.

Calahonda52 · 29-03-2019 1:20pm

Go for a rain screen design, fit windows on outside face of blockwork.
Less blocks does not mean less cost.

What is your ACH target for airtightness

BryanF · 29-03-2019 4:21pm

Go wide insulated cavity or EWI, don’t mix both

Don’t leave an un-insulated cavity inside the insulated envelope,

your air-tightness/vapour barrier layer would need to be on the outer block leaf,

thereby defeating the purpose of a vented/draining cavity.

If you must use concrete blocks then just go with an insulated cavity, or ewi with block on flat, either can be detailed to avoid thermal bridging and designed to deal with the weather.

blahfckingblah · 01-04-2019 7:47pm

Recent experience of issues with insulation boards getting damaged during construction, mortar droppings preventing snug fit at board joints, messy cuts, boards not sitting flush with the inner leaf etc. has led me to question whether we should be using this method at all.

I'll definitely be looking into external insulation or pumped cavities with a view to reducing these issues in future.

What are your preferences?

Jcanty85 · 07-04-2019 3:55pm

I'm leaning towards ewi, can buy 150 eps for approx €13 per sq m supply only. We have so many windows across the southern aspect I thought it would be a good option so I wouldn have to be constantly watching blocklayers. Plus as we both work full time we would only be able to inspect in the evening after the wall is built so I thought this would be a good option. Just not sure about the wall construction, for simplicity I'd love to go with precast panels but they are just too expensive compared to block work so maybe a 200 mm wall (two blocks on edge as opposed to a 225 block on flat). What would be other options I wonder?

BryanF · 07-04-2019 11:12pm

Suggest you get reputable system supplied and installed by installer. with joint warrant between installer & manufacture

Beasky · 28-07-2019 8:32pm

Hi Jcanty,

Have you started your house yet. We are in the process of building a block on flat externally insulated house. The price of EWI seems to have gone up substantially. We got a quote last year which we used as our baseline, however a repricing in July was 50% more- just something to note. Its too late for us to change tact now and will have to carry the cost. We have also tried to get quotes from different installers and have only got one proper quote back and another very vague quote based on cost per square metre but will not price from our drawings.

We had also wanted to go down the route of precast but could not find a willing supplier. We have used precast floors though and stairs.

Currently at first floor and blockwork to roof starts next week

Happy to share our experience.

Calahonda52 · 29-07-2019 9:33am

Beasky wrote: »

Hi Jcanty,

Have you started your house yet. We are in the process of building a block on flat externally insulated house. The price of EWI seems to have gone up substantially. We got a quote last year which we used as our baseline, however a repricing in July was 50% more- just something to note. Its too late for us to change tact now and will have to carry the cost. We have also tried to get quotes from different installers and have only got one proper quote back and another very vague quote based on cost per square metre but will not price from our drawings.

We had also wanted to go down the route of precast but could not find a willing supplier. We have used precast floors though and stairs.

Currently at first floor and blockwork to roof starts next week

Happy to share our experience.

Where are you fixing the windows: on outside of wall before ewi goes on?

Beasky · 29-07-2019 11:45am

We are fixing on the outside of wall but sitting on outer edge

Calahonda52 · 29-07-2019 4:28pm

Beasky wrote: »

We are fixing on the outside of wall but sitting on outer edge

Fixing on the outside face reduces the thermal bridges and make the detailing easier.

Think through the detail.
A guy called SAS on here did it about 10 years ago

Carbonnet · 12-10-2019 10:26am

Life time of system? - will you get 30 years? Check the Agreement Certification - read the maintenance schedule to achieve the 30 years. 30 years might seem a long time - but its probably just after your mortgage finishes. Be mindful.

External wall insulation

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