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New build - External wall insulation

Bigman87

Hi all,

I am currently starting the process of building my own home on my parents land. I have just received planning permission and am looking at various construction methods. I want to try build to passive house standards, keeping it well insulated and airtight.

I am keen on using a single leaf thermal block with external wall insulation and a render finish, rather than using the typical cavity wall construction. My father is a blocklayer and he is onboard with me to use this method.

I am looking at Mannoks SIMS product: https://www.selfbuildwithmannok.com/sims-for-self-build

I am looking for advice/tips from anyone who may have used this method in their new build.

I do not intend to go with a timber frame build or ICF construction.

Thanks

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windowcills

How strong is external insulation, if you have a kid who want to kick a ball against a wall in the evenings do you have to tell him/her to go inside and play on their ipad instead

Biker1

https://www.boards.ie/discussion/2058316248/new-build-external-wall-insulation

Excellent choice of building system if you want to go the Passive House route. Use an insulated raft foundation as well. As for the strength of the external insulation don't believe the people who say it cant handle football impact.

andyd12

In the same situation as the OP, keen to use a similar solution rather going down the cavity wall route which has many cold bridging spots

Lumen

https://www.boards.ie/discussion/comment/121179809#Comment_121179809

True, it's a shame there are only two forms of entertainment in the world, ipads and kicking balls against walls. Hopefully once we get to Mars someone will have figured out a third one.

Anyway, if you want a ball wall, just throw a load of blocks up freestanding in the garden, rather than compromising the house build.

(FWIW external insulation is often reinforced with mesh in areas that need it)

adriant900

What is the cost difference between standard cavity wall and what your suggesting? Would you think about standard block but on the flat with external insulation? Could up the external insulation to make up for it?

Any reason your not interested in timber frame and ICF?

Calahonda52

OP where is the house located?

How exposed is it?

I don't agree with my learned friends here re the robustness of normal EWI to footballs, hurley balls, basket balls etc.

My go to solution in exposed sites or where 'balls will be an issue s a ventilated cavity behind cement board.

The other question I have is how airtight are the blocks?

Then can you chase them for services without impacting the thermal performance.

Finally how are they on sound transmission vs concrete block.

I concur with avoiding a cavity wall.

adriant900

https://www.boards.ie/discussion/comment/121200803#Comment_121200803

Why are ye so keen on avoiding cavity walls?

If you go with the thermal block, how do you reassure yourself of the standard of the material, you don't want to end up like the people in Donegal who built with poor quality blocks or the schools in the UK that are closed because of poor reinforced aircreed blocks. Of cource very unlikely to repeat itself but just looking to learn what we can to be sure that it doesn't happen to us?

bfclancy2

https://www.boards.ie/discussion/comment/121201063#Comment_121201063

the blocks used in donegal were standard concrete blocks

adriant900

Yes correct, I knew that but didn't make it clear. Same question applies, how do we know that the quality of the materials that we are using?

andyd12

I have done some research and here is my 2 cents

I am strongly considering Mannok 210 mm block with EWI for my new build. My father is a blocklayer and he knows the traditional cavity is an outdated method of building.

Aircrete Blocks from Mannok

https://www.mannokbuild.com/aircrete-thermal-blocks/

Mannok aircrete blocks - The simple way to achieve thermal excellence. Lightweight, high performance thermal blocks which are precision manufactured using autoclaved aerated concrete (AAC) by advanced technical processes. For thermal performance, strength and durability, Mannok aircrete blocks are the best in Ireland

215 mm Mannok block is 3.90 ex VAT per block.

100 mm Standard block is .66c ex VAT per block.

There will 2/3rd as many blocks in the rising walls using the Mannok method. Plus, you dont need to use the Mannok blocks in the rising walls, just standard blocks.

Half as many blocks above the ground using the Mannok method on external walls. Internal walls don't need to be Mannok blocks only the first course.

The gap in price between Mannok and standard block considerably closes factoring all in above.

Mannok block work will be quicker, cleaner, easier, straighter lines etc particularity around windows and doors

Speaking of insulation:

EWI method is slow and somewhat expensive but so is insulated internal wall slabs. Also factoring in the cost of cavity wall insulation, wall ties etc.

EWI moves the dew point to outside and reduces the need to address cold bridging massively inside.

A 215 mm Mannok block with 200 mm insulation achieves a U-value of circa 0.13. No insulation internally

A 215 mm Mannok block with 250 mm insulation achieves a U-value of circa 0.11. No insulation internally

These are below passive house U-values.

I cannot see the advantage of traditional cavity over a Mannok type method factoring all of the above in.

Granted lashing the wall with a sliotar is a consideration but surely can be worked around

redsheeps

https://www.boards.ie/discussion/2058316248/new-build-external-wall-insulation

I know it's only a month ago you posted but curious how you're getting on with this planned approach?

We're aiming for A2 and are currently getting construction drawings completed and getting conflicting advice about the insulation process between architect doing the drawings and builders + builder surveyor. Architect is advising what you're planning to do (didn't specifically mention Mannok though) while the builders and a building surveyor we've spoke to all say the EWI approach is for retrofits, and are advising cavity platinum bead with internal insulation.

Architect said we'll get condensation and mould overtime with cavity, and the EWI will push dew point outside the house and avoid condensation and mould. Two BER guys I spoke to both said the condensation/mould issue with cavity only happens if you go OTT with the internal insulation; they said to keep internal insulation at a maximum of 62.5mm, anything above this will cause the condensation and mould growth; stay under this and we'll be fine.

Across five local builders, all recommended to us, only one has done a new build house wtih EWI and he mentioned that it still only got to A2 rated. The architect in fairness did say you want a builder who is comfortable to complete the work using single leaf with EWI and we haven't found one. Your father being a block layer sounds like a real bonus as it sounds like he's comfortable going with this 'new' approach.

Bigman87

There does not seem to be too many houses being built at present using EWI, more so using the typical cavity wall construction. Having spoken to a few different professionals in the construction industry there is quite a mixed opinion on EWI for new builds.

I have looked into the EWI method in great detail over the past while and have reached out to a few companies for quotes for supply and install. I do think it is a good method as good U values can be achieved across the wall section, it reduces the effect of thermal bridging and as you mentioned it pushes the dew point to the outside. But the cost of it is not selling it for me. I received a quote from a company for 32k for supply and install for EWI.

I have reached out to companies doing the pumped cavity insulation and received quotes for 4.5k. This is a 200mm pumped cavity. I was able to calculate the number of insulated plasterboards (92.5mm) required and it is costing approx 6k. I plan to do this work myself. Then the external plastering should not cost more than 7k. This is working out to be approx 18k, quite a substantial price difference between the two methods.

I am able to achieve a U value of 0.10W/m²K using the cavity method, which is pretty good in my opinion.

Regarding your BER accessors comment for internal insulation, I don't see how going with anything below 62.5mm is a better choice for condensation or mould, surely the greater the depth of insulation is better for reducing heat loss and avoiding condensation/mould issues. Maybe I am missing something here.

I plan to look a bit more into the pumped cavity method to ensure I avoid condensation issues down the line but for now it is what I am strongly considering more so than EWI.

MicktheMan

https://www.boards.ie/discussion/comment/121370834#Comment_121370834

and are advising cavity platinum bead with internal insulation

Nooooooooooo. Awful advice!

Literally just in the door from surveying a house with this exact wall buildup. They thought they were doing the right thing when they built because of the 'A' BER cert rating. Air to water heat pump / underfloor heating / MVHR etc. The reason they called me is because their esb bills are mental AND they don't feel comfortable! Their exact words after the survey: "had we known then what we know now we would have done it very differently".

andyd12

https://www.boards.ie/discussion/comment/121373480#Comment_121373480

What method do you recommend then?

With either system, the u-values stack up both below 0.15. High electricity bills in a house with this level of insulation makes me think air tightness is very poor and/or the heating system is poorly designed /installed

MicktheMan

https://www.boards.ie/discussion/comment/121373536#Comment_121373536

Simples. Block on flat, sand/cement rendered internally and ewi outside. Window frames flush to outside of block wall allowing full overlap with ewi.

Deals pretty well with thermal bridging, air tightness and all layers are clearly visible so practically impossible to f**kup on site. Adds thermal mass inside and moves the wall dewpoint to outside the blockwork so safe from that pov too.

Correct about airtightness in the house I visited although passed the b.regs for year of build. However, the insulated board installation over the bare block internal leaf had a large role to play in the airtightness issue (sure, why plaster a block wall that gonna be boarded over anyway!). End result; super insulated "A" rated house which is cold/uncomfortable and/or expensive to run.

hydrus21

have reached out to companies doing the pumped cavity insulation and received quotes for 4.5k. This is a 200mm pumped

Could you elaborate please.

Is this 200mm empty cavity or part empty and what is the m2

Of the walls? Thanks

andyd12

https://www.boards.ie/discussion/comment/121373601#Comment_121373601

What thickness insulation did they use in the cavity and on the insulated slab?

Likewise with the floor and ceiling insulation

A lot variables here at play but substandard air tightness, plumbing and possibly mvhr are all likely factors here.

MakersMark

My new build in Germany has 200m EWI with skimcoat of plaster to protect from the elements.

Most comfortable house I've ever lived in.

MicktheMan

https://www.boards.ie/discussion/comment/121376733#Comment_121376733

150mm cavity, 50mm insulated slab and not sure on floor tbh.

KingPanko

https://www.boards.ie/discussion/comment/121373480#Comment_121373480

What did they do wrong?

MicktheMan

https://www.boards.ie/discussion/comment/121388638#Comment_121388638

Neither the architect or the project manager really understood how to achieve a decent airtightness level.

redsheeps

https://www.boards.ie/discussion/comment/121373480#Comment_121373480

Wasn't getting notifications of replies to this query. Cheers for advice.

What we're struggling with is we have family who built their house using the same method we've been advised to go with (cavity + internal). Their house is like a furnace. In the summer they're not able to sleep in their south facing rooms because of the heat build up. Their house was built 10 years ago now.

It's been a real PITA to make a call on this. Literally every builder, every BER assessor, and a building surveyor recommended cavity + internal. One other surveyor said to go with rigid insulation in the cavity, but everything I read on that says to stay away from it as it's took difficult to get it done right and avoid thermal bridging.

andyd12

https://www.boards.ie/discussion/comment/121455022#Comment_121455022

I think the biggest problem is with the bedrooms being south facing.

If the house was externally or internally insulated, the bedrooms would be still be warm. Either method gets similar U-values.

Outside a ball hitting the wall. I really can't find fault with EWI

Lumen

https://www.boards.ie/discussion/comment/121516244#Comment_121516244

I understand that daytime overheating can be blamed on solar gain, that clearly isn't happening at night time. Overnight temperatures in summer are below comfortable room temperature.

So what's the cause in this case (of internal+cavity insulation)? Heat soak from overheated external walls? Insufficient ventilation?

bigmcm88

@MicktheMan Really good to see I'm not the only person thinking block on flat with EWI is sufficient. I've a few things that still make me hesitant though as I get into a design stage soon...

1. Are you using standard 4in or mannock 4in? I'm hoping standard cause the mannocks are out of my league except for the base rings? Would you recommend a sand/cement render on the outside of the leaf also before the EWI slab, because there's no air tightness membrane?

2. Do you need passive sills with the windows then as standard sills become a thermal highway or what other options are there?

3. How complex does the cold bridging get at the wall plate / roof meet point?

4. I love my stone fronting. Have you ever come across an EWI finish that has stone outside? I'm thinking there's surely some way of fixing ties to the EWI slab and the using a lime mortar bond to have a dry stone wall look? It would give a solid finish and protect the EWI slab.... then again it could just sound crazy ,, I'd be interested to know thoughts on same

andyd12

https://www.boards.ie/discussion/comment/121551876#Comment_121551876

215mm standard block with 200mm EWI will achieve roughly a u-value of 0.145

215mm mannok block with 200mm EWI will achieve roughly a u-value of 0.13

1. I will be using a mannok(thermal) for the base rings. Why render on the outside? Sand/cement will be used in the scratch coat for internal skimming.

2. I will not be using passive sills but aluminum folded. They are stuck on underneath the window. Very minimal thermal bridge.

3. Not too complex. Feel free to PM, I can send over details via email.

4. The weight of the stone would be a big issue. A wider foundation and rising wall is used with stone. Perhaps the use a non-thermal conductive ties from the block work through the insulation to help tie it in?

andyd12

What are peoples thoughts on ESB meter box location with EWI?

listermint

https://www.boards.ie/discussion/comment/121821368#Comment_121821368

I think the suppliers should start making deeper poxy cabinets.

andyd12

Sorry I should have said for new builds.

The meter box is 155mm deep. With 200mm EWI, this would leave 45 mm insulation behind the meter.

Bigman87

Could the meter box be situated in the garage wall? I'm not sure of the implications of doing this but could be a potential alternative.