External Insulation for a New Build House

JD6910

hi guys,

i am starting the building process over the next few weeks:D and was considering doing the following:

cavity wall construction with standard concrete blocks (not thermal blocks due to cost)
200MM cavity fully pumped
100MM external wall insulation wrapping the entire house also.

this may be over kill but i am keen to "future proof" the house;).

the reason i am going for the "traditional" cavity wall is that the house is in an exposed location and i am nervious of water ingress. i think the external insulation along with the fully pumped cavity should prevent any water travelling accross to the inside and also give the house serious insulation and future proof it.

any thoughts on this????

fclauson

JD6910 wrote: »

hi guys,

i am starting the building process over the next few weeks:D and was considering doing the following:

cavity wall construction with standard concrete blocks (not thermal blocks due to cost)
200MM cavity fully pumped
100MM external wall insulation wrapping the entire house also.

this may be over kill but i am keen to "future proof" the house;).

the reason i am going for the "traditional" cavity wall is that the house is in an exposed location and i am nervious of water ingress. i think the external insulation along with the fully pumped cavity should prevent any water travelling accross to the inside and also give the house serious insulation and future proof it.

any thoughts on this????

Congrats on getting planning - but some thoughts
EWI is not cheap - I would get a QS to price out the options your are thinking about before you dig a single sod or lay a single block - best €800 I spent on the whole build
You will need to see where the dew point falls - to check for internal condensation
You will need to detail out doors, windows, eve sand all other opes before you start - get professional advice on this - a single block or tape in the wrong place will cause no end of issues

Just to warn you it took as 11 months of detailing post planning before we started - and to date we have had not headaches on site :P (but I am not being complasant we are still chasing detail before we get there)

And with all the good weather we are 2 weeks ahead of shedule

fclauson

plus check every NSAI and BBA cert before you use any products

SAS (on this forum) is the expert end user for EWI who has made many posts on the little challenges he has faced

sas

fclauson wrote: »

SAS (on this forum) is the expert end user for EWI who has made many posts on the little challenges he has faced

Let's knock that one on the head right now

I am officially anti EWI for new builds. Great for retrofit, stay away from it for new build.

There are alots of companies doing it and very few of them do it well from what I've seen. Those that do it well, charge more because it's more labour intensive.

EWI offers alot but durability is an issue.

The final straw for me came 2 weeks ago. I noticed that the render had gotten a 4 inch scrape at 1 location. It only took the texture off the render at that point but it really drove it home to me. I can't repair that cheaply. I have to buy a bucket of render which is €300+. It's also not the case that I can buy a bucket and keep it in reserve for down the line. I have a bucket from last september which was half used and it's now fully green, it was white in september. The damage is entirely superficial so I'm just going to leave it. It's damn annoying though.

No system is perfect but I'll bounce you back to fclauson and suggest you seriously look at wide cavity. Just give it a few months until he's worked out how to safely mount his windows

muffler

JD6910 wrote: »

i think the external insulation along with the fully pumped cavity should prevent any water travelling accross to the inside and also give the house serious insulation and future proof it.

Just to point out the obvious......insulation wont prevent water penetration.

sas

muffler wrote: »

Just to point out the obvious......insulation wont prevent water penetration.

In theory (and it better be in practise), EWI is a water proofing layer i.e. no cavity used.

I assume that's what the OP is thinking about.

JD6910

folks many thanks for the replies.

the way i look at EWI is - with a new build i have to plaster the house regardless - i plan to take that plastering money and put it towards the cost of EWI. surely this makes sense??

sas - can you expand on why you are anti EWi for new builds?

muffler - i agree insulation wont prevent water ingress but EWI is waterproof?? also my theory is by filling the cavity i wont have air movement in the cavity and this could be massive in my very exposed site.

sas

JD6910 wrote: »

folks many thanks for the replies.

the way i look at EWI is - with a new build i have to plaster the house regardless - i plan to take that plastering money and put it towards the cost of EWI. surely this makes sense??

sas - can you expand on why you are anti EWi for new builds?

I paid 42k for my EWI job. You won't pay that to have your house plastered. You might expect to pay 5k in the current climate for plastering labour for outside. Sand and cement isn't that expensive. Neither is paint.

Don't be under the impression that because you are going for 100mm EWI, that it would be much cheaper than 300mm for example. The cost in EWI is labour first (which is not really affected by insulation thickness), then render\adhesives and finally the insulation itself. The only item that can be cost dependent on insulation thickness (apart from the insulation itself) is the mechanical fixings if they are required. The longer they are, the more expensive they get.

With new builds you have all the options in the world. If the structure is already up (i.e retrofit) then you're more restricted and EWI becomes more viable from a performance point of view.

Durability is my issue with EWI and the cost implications of even the smallest repairs. Also the cost of the system in general. Yes it offers the possibility of an thermal bridge free facade.

JD6910

cheers for that sas.

fortunately i am getting a deal and the maths all add up!!!
just wondering from a "technical" point of view if it makes sense?

the house is not built yet and i am trying to make all these decisions now before i start so that i can detail all the tricky bits correctly!!!!

any thoughts on the pumped cavity with the EWI?

sydthebeat

JD6910 wrote: »

any thoughts on the pumped cavity with the EWI?

doesnt make any sense on a new build.

the same performing wall can be constructed simply by widening the cavity....... at very significant less cost.

Id trust a cavity wall pumped over an EWI house in an exposed area every time.

JD6910

surely the EWI gets rid of all thermal bridging issues?

i would have thought the EWI is a better insulator than the cavity wall?

i am nervious of a pumped cavity wall on its own in case water gets accross to the inside. the EWI would act as a water barrier also.

Do-more

EWI is the last thing in the world I would be jumping at a "deal" on.

Have a read through this thread for instance, lots of links to studies of failed EWI towards the end of it.

As SAS has pointed out installing EWI properly is very time consuming and the areas which are prone to fail are around doors and windows and at other junctions.

If you get cracks in the render at the corners of windows for example then you will get water penetration, particularly if as you say you are in an exposed location.

Once you get water in behind your EWI you are opening yourself up to all sorts of possible problems down the line.

EWI doesn't give you a solid stable base to apply render too, you will always be prone to the possibility of cracks appearing in the problem areas due to variations in the weather.

You are much better off forgetting about the EWI IMO and sticking with a wide cavity where you have a nice stable base to apply your plaster too and which should weather significantly better in the future.

sydthebeat

JD6910 wrote: »

surely the EWI gets rid of all thermal bridging issues?

passive houses are now built with cavity walls with no thermal bridges.

JD6910 wrote: »

i would have thought the EWI is a better insulator than the cavity wall?
.

no, why would you have thought that?

i said "the same performing wall" .... the extra thermal resistance you get from the EWI can be incorporated into the cavity. The basic rule of thumb with insulation is to try to keep it all in the one plane. Otherwise you get increased risks of interstitial condensation issues.

JD6910 wrote: »

i am nervious of a pumped cavity wall on its own in case water gets accross to the inside. the EWI would act as a water barrier also.

EWI is generally a waterproofing render on expanded polystyrene blocks glued together on a block wall. A cavity wall is a water proofing render on a concrete block with polystyrene insulation with Damp proof courses, trays etc.
why do you think EWI would be more robust?

JD6910

just to clarify - please ignore all cost issues - have a plan here that makes finacial sense this is why it is so tempting!!!
the cost price for EWI versus the normal plastering price are close, and therefore is sounding like a no-brainer???

surely the 200mm pumped cavity along with the EWI is a future proof job.
i reckon we will be here in 5 years time saying - rememeber when we used to install only 200mm in the cavity!!!!!

any other suggestions for future proofing taking into account my links to cost price insulation products??

muffler

JD6910 wrote: »

rememeber when we used to install only 200mm in the cavity!!!!!

Eh? They haven't even started that in Donegal yet

sas

JD6910 wrote: »

the cost price for EWI versus the normal plastering price are close, and therefore is sounding like a no-brainer???

If you are getting a similar price for these then you are either getting the most expensive plasterer in the country for the normal plastering or you are getting an EWI job that you wouldn't want.

No way in hell they should be priced similarly.

JD6910

when you take into account the labour, sand, cement, waterproofer, beads etc... and the cost price of EWI - they are close.

taking into account also that the cost price for EWI is very low and those guys are on big margins!!!!!

assuming the cost issue is sorted and they are close - would you put it in??

sas

JD6910 wrote: »

when you take into account the labour, sand, cement, waterproofer, beads etc... and the cost price of EWI - they are close.
taking into account also that the cost price for EWI is very low and those guys are on big margins!!!!!

The only reason I'm not letting this go is so that someone else won't read your posts and think they are accurate.

EWI materials (render only) are multiples of the cost of materials for sand and cement. I priced materials too both here and in Germany.

Then you have the insulation and adhesive in the EWI job.

The labour for applying the EWI render may be equivalent to regular sand and cement.

Applying the insulation is the labour intensive part of EWI though. 6 weeks on my house. Plastered in 1 week.

Those guys are not on big margins anymore I can assure you. It's a race to the bottom quality wise in EWI.

I wouldn't use EWI due to the cost of small repairs. I'd go with a 250 - 300mm cavity. However, as you appear to have found the most cost effective EWI system on the planet, this isn't really going to help your decision making.

Good luck with your project, I genuinely hope it works out for you.

JD6910

steady sas!!!!

leave the cost issue to me. no one should take my cost issue as a rule of thumb as all deals very -obviously.

all things being equal it sounds like you would opt for the pumped cavity option - thanks for your thoughts on that.

i too have fears about EWI strenght but at the cost i am getting it done for, its hard not to consider it!!!!

muffler

JD6910 wrote: »

but at the cost i am getting it done for, its hard not to consider it!!!!

Do you mind telling us the cost and the surface area involved?

JD6910

sorry muffler - i could tell you but as the old saying goes.... then id have to kill ya!!!!!!

leaving cost aside - is EWI a good idea on a new build.

the 200mm cavity pumped with 100MM EWI gives a u-value of 0.11.

Do-more

JD6910 wrote: »

leaving cost aside - is EWI a good idea on a new build.

sas wrote: »

I am officially anti EWI for new builds. Great for retrofit, stay away from it for new build.

And that is coming directly from a guy who has used it on a new build.

sydthebeat wrote: »

doesnt make any sense on a new build.

Coming from an industry professional.

Look back through this thread, no one has suggested it is a good idea.

JD6910

Look back through this thread, no one has suggested it is a good idea.

thats the confusing bit - EWI is highly recommended for retrofit or on an existing house but not on a new build??????????????????????????????

surely EWI has the same advantages on a new build as it does on an existing house???

fclauson

JD6910 wrote: »

....
the 200mm cavity pumped with 100MM EWI gives a u-value of 0.11.

250mm cav fully pumped is 0.13 ish (depending on wall ties)

down at these levels its a little academic as to which 0.11,12,13 you go for its more about its implementaiton on site (e.g. windows installs, door thresholds, fabric performation cold bridge limitations, solar gain etc) and your overall building plan

From the investigations I did - I decided on a 250mm cav - its a bungalow the roof and floor are each 34% of exposed area (i.e. 68% total)
the walls is 24%
the glazing is 7%

So my walls actually only make up 1/4 of my exposed surface - I focused my money on the roof and floor more than the walls - I could have gone for a 300mm cav but on balance I think I chose about right

My build is about 15kWh/m2 (glazing g value making the big difference - g value of 40% its about 19kWh and 61% its about 14) - so about passive standard - but will not be certified.

The variation in my expected heating bill by tweeking at this level is in the 10s of euro not 100s - and the item to impact the most will be the peope/usage and not the fabric

fclauson

JD6910 wrote: »

thats the confusing bit - EWI is highly recommended for retrofit or on an existing house but not on a new build??????????????????????????????

surely EWI has the same advantages on a new build as it does on an existing house???

No - on a retro fit changing to a 250mm fully pumped cavity from a 200mm solid block construciton is not possible - so EWI works - on a new build you have choice, value for money, implementation ease, design preference .......

dfader

fclauson wrote: »

JD6910 wrote: »

....
the 200mm cavity pumped with 100MM EWI gives a u-value of 0.11.

250mm cav fully pumped is 0.13 ish (depending on wall ties)

down at these levels its a little academic as to which 0.11,12,13 you go for its more about its implementaiton on site (e.g. windows installs, door thresholds, fabric performation cold bridge limitations, solar gain etc) and your overall building plan

From the investigations I did - I decided on a 250mm cav - its a bungalow the roof and floor are each 34% of exposed area (i.e. 68% total)
the walls is 24%
the glazing is 7%

So my walls actually only make up 1/4 of my exposed surface - I focused my money on the roof and floor more than the walls - I could have gone for a 300mm cav but on balance I think I chose about right

My build is about 15kWh/m2 (glazing g value making the big difference - g value of 40% its about 19kWh and 61% its about 14) - so about passive standard - but will not be certified.

The variation in my expected heating bill by tweeking at this level is in the 10s of euro not 100s - and the item to impact the most will be the peope/usage and not the fabric

Fclauson,
We have more or less decided on wide cavity for our new build. Wont be starting for a while though. the only thing thats really bugging me though is getting a good detail finalised for fixing windows and closing the cavities at opes. would be great to see what youve done when you get to that stage. Also before mods say your architect or engineer should advise i want to research this myself as theres lots of details out there so looking for best.
thanks
dfader

fclauson

PM Sent

kboc

fclauson wrote: »

PM Sent

FC
Could you pm me that also, if you don't mind

Thanks
K

fozz10

sas wrote: »

Let's knock that one on the head right now

I am officially anti EWI for new builds. Great for retrofit, stay away from it for new build.

There are alots of companies doing it and very few of them do it well from what I've seen. Those that do it well, charge more because it's more labour intensive.

EWI offers alot but durability is an issue.

The final straw for me came 2 weeks ago. I noticed that the render had gotten a 4 inch scrape at 1 location. It only took the texture off the render at that point but it really drove it home to me. I can't repair that cheaply. I have to buy a bucket of render which is €300+. It's also not the case that I can buy a bucket and keep it in reserve for down the line. I have a bucket from last september which was half used and it's now fully green, it was white in september. The damage is entirely superficial so I'm just going to leave it. It's damn annoying though.

No system is perfect but I'll bounce you back to fclauson and suggest you seriously look at wide cavity. Just give it a few months until he's worked out how to safely mount his windows

i have a lot of experience plastering for a EWI company and im interested what bucket costs E300?? i assume your talking about a bucket of coloured acrylic finish coat?

Ex factor

Sas , I can see now why it cost you 42 k for your Ewi when a 70 - 80 euro bucket is costing you e300.
Minor repairs ie 4 inch scratch can be done DIY surely , mastic around damaged area and brush in the acrylic , if its only a scratch . The discoloured previous bucket should in most cases only need a good mix up , if kept indoors since first applied , it's essentially paint that needs a good stir up