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air-tightness with external insulation

timmer3

i have an end of terrace house. recently had the gable wall insulated with 120mm EPS. originally i only did this wall because it was as much as the SEI grant would cover and i didn't realistically consider doing the front and back walls as well due to cost and also the aesthetic of making the house "fat" compared with the rest of the terrace. but now looking at it long term, the benefit of keeping the thermal mass of the walls, keeping the room space, factoring in the cost of a breathable dry-lining system, i'm just going to bite the bullet and insulate the front and back extenrally as well. my installer has hooked up with a new supplier and is offering 55mm XPS delivering the same .27 U-values as the 120mm XPS. this will reduce the profile of the insulation to near negligible (if i remove the pebble dash at 20mm depth) which is great. i'm currently awaiting a quote.
in the meantime, i'm trying to plan the air-tightness for the house, i'm using HRV and want to make the house reasonably air-tight. Roof and ground floor will obviously need an air-tight membrane. for the walls, i'm leaning towards removing all the existing plasterboard as it is in mixed condition anyway, so i have the option of installing a membrane if necessary.
i read somewhere (i think it was construct ireland issue 7) that a house wrapped in EPS would have an air-tightness of about 3 without any air membranes. i would hope to get a lower ACH figure than this, i would be very happy to get around 1 for the house to make the HRV reasonably efficient. is this possible without a membrane on the walls (which are 10 inch poured concrete)?
also, will the choice of plasterboard make any difference? i'd prefer not to have to skim unless i really have to, if i was going to hire a plasterer to skim the entire house (at least €1000 i'd say) i'd probably rather spend on the money on fermacell.
last thing... should i consider an air-tight membrane for the party wall?

many thanks for any advice.

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Comments

sinnerboy

Careful - sounds like the other installer is going to use a PIR board in liue of polystyrene to reduce on thickness . The IAB cert for one the the systems removed PIR from the scope of certification ( unstable , cracking render )

Air tightness is all about keeping the internal air internal . So stopping leaks at the internal surface is the aim . So linking air tightness to any external surface treatment is flawed thinking wherever you read it ( I am a fan of CI )

An AT result of 1 would be incredible without the determined efforts of an experience passiv house builder . If you get 5 - be happy and proceed with hrv .

Replace your plasterboard with wet applied plaster . If you can stomach it remove sufficient ceilings to plaster in between the joists where they rest on the walls

Tape seal windows and external doors to the block wall before plastering

If you have any recessed lighting - remove it in favor of surface mounted fittings

It would pay to to have the house tested before significant works are done

timmer3

thanks a million for the reply. that's great advice. i guess i was being a bit ambitious with the level of air-tightness then.
the supplier mentioned that IAB approval was pending, he said they currently didn't have the facilities to test it in Ireland, and would charge €20k to have it tested and approved, where they would only send it back to the facility in europe where it is already tested and approved to european standards. he sounded sure that SEI were in the process of adding it as an approved external insulation type. i haven't got the spec on it yet but he's sending me a link later on. he referred to it as 'blue boards' and said it was an XPS type insulation, the latest technology etc. but thanks for the caution, i always do a lot of research before using any materials with the house.

with the air-tightness i was actually suggesting to install it on the inner face of the wall behind the plasterboard, sorry if i didn't make that more clear. The figure of 3 i believe was referring to the natural air-tightness of a concrete wall insulated externally with EPS, with no membrane anywhere. most of the articles etc that i've read are all to do with combined dry-lining and air-tightness so i was interested to see what the recommendation is regarding the walls of an externally insulated house. ceilings are half ripped out already and i'll be removing the rest completely, they're old and cracked etc. i figure the house is 60 years old and i want to invest in it now to make it last another 60 years. i don't plan on being a perpetual renovator and decorator like you see some people changing their kitchens and decor every few years! but you never know, situations change etc.

can i ask what the benefit of a blower test is before the works are done? surely it would just prove the point that the house is totally porous? at the moment there is no floor or attic insulation and the floorboards are half loose due to wall knockouts and electricians etc. it's totally draughty. before i bought the house a structural surveyor did a layman's BER estimate on it and he put it at an E.

sinnerboy

if the house is so ripped apart - an AT test is of no value alright . But line up a test now . Ask one or two testers to site now . They are good guys to give practical advice site specific .

Do not touch any system that is not IAB certified . Forget pending . SEI wont pay any grant on this basis . As a certifying architect - I would not entertain it .

Your hrv filters will need regular cleaning . Several times per year . Bear this in mind when you locate the fan unit .

timmer3

definitely agree re: IAB certification. am waiting to see what the system is before i will even go near accepting a quote. i'll also run it by my architect of course. many thanks for the pointers.

Carlow52

Interesting post.

Had never considered just doing the gable in an external Insulation job.

Would welcome any comments as it does not seem intuitive as an idea.

timmer3

it suited my house perfectly because the gable wall is north facing, and all the heat gets sucked out that wall in the winter. also the stairs are on the gable wall so it is much more difficult and expensive to do a proper dry lining job there.

i would have cold bridging and condensation issues at the junction with the warm wall and the cold (dry-lined) wall, but i was prepared to deal with that via HRV which i hoped would extract any damp from the walls quickly. this is not speaking from experience. with the SEI grants available this year, 4k towards insulating your home with the optimal insulation type is not to be sneezed at. in my case, it cost 4k to insulate the gable wall, and so far it's looking like SEI will honour the grant in full but i am currently awaiting payment from them.

a dublin semi-D house in the current issue of Construct Ireland did the same thing, the author of the article concluded that a combination of insulation types might become the norm as restrictions often apply re: front of house etc.

trevdahead

timmer3 wrote: »

it suited my house perfectly because the gable wall is north facing, and all the heat gets sucked out that wall in the winter. also the stairs are on the gable wall so it is much more difficult and expensive to do a proper dry lining job there.

i would have cold bridging and condensation issues at the junction with the warm wall and the cold (dry-lined) wall, but i was prepared to deal with that via HRV which i hoped would extract any damp from the walls quickly. this is not speaking from experience. with the SEI grants available this year, 4k towards insulating your home with the optimal insulation type is not to be sneezed at. in my case, it cost 4k to insulate the gable wall, and so far it's looking like SEI will honour the grant in full but i am currently awaiting payment from them.

a dublin semi-D house in the current issue of Construct Ireland did the same thing, the author of the article concluded that a combination of insulation types might become the norm as restrictions often apply re: front of house etc.

hi there
did your contractor tell you that you would get the grant.if so then they have mislead you.you can only receive the grant if you have 100% of your walls insulated,partial insulation due to finacial constraints will not be grant aided.check the sei website for the partial solutions.
how did your contractor fill out the form?did they state that 100% of the house was insulated if so they have broken their contractor conditions.
if and it may be a big if the sei come a check your property they will see that you have only completed partial insulation your grant will be void

PCPL

Hi, just to clarify, to qualify for the SEI grant 75% of the wall area of the house must be insulated, if the contractor said you would get the full €4000 he has led you astray im afraid.

Also a point on the PIR insulation being unstable, was it not the kingspan K5 board which was found to be unstable? I stand to be corrected on this

trevdahead

PCPL wrote: »

Hi, just to clarify, to qualify for the SEI grant 75% of the wall area of the house must be insulated, if the contractor said you would get the full €4000 he has led you astray im afraid.

Also a point on the PIR insulation being unstable, was it not the kingspan K5 board which was found to be unstable? I stand to be corrected on this

you must insulte 100% of the walls.it has to be a full solution

there has been no definative reason as to why the k5 has been withrawn by the iab.but ive never heard of it being unstable

timmer3

please give me a little credit. i am not the type to splash 4000 euros on maybe getting the grant. i did my research and hired the contractor to do the work, having received confirmation from SEI (twice) before getting the work done and made sure that their conditions were satisfied. i would also never submit a dishonest form saying 100% of the wall was insulated when it wasn't. i worked out the area and it was about 55% which was put on the form. just to clarify it is the home owner who fills out (and submits) the declaration of works form, there are 2 or 3 boxes for the contractor but it is the responsability of the homeowner to ensure the information is correct.
at the time i got the grant approval (early april/may) there was plenty of confusion between SEI and the contractors, with conflicting reports about what was possible with the grant and partial insulation. since then they have published a revised policy on partial insulation which is much stricter than originally advertised. however i believe they will honour the grant as they said they would. this is based on implementing complete wall insulation for the house, on the form i said i would be dry-lining the remaining walls at my own expense, and this was one of the conditions they said, as long as the entire house was being insulated that was fine, and that i would only qualify for grant assistance for one type of wall insulation. i also noted on the form that it would disturb the line of the terrace to insulate the front and back of the house at 120mm.
it's possible i'll be insulating the front and back externally anyway but either way i will not be dishonouring my side of the bargain with SEI.

trevdahead

timmer3 wrote: »

please give me a little credit. i am not the type to splash 4000 euros on maybe getting the grant. i did my research and hired the contractor to do the work, having received confirmation from SEI (twice) before getting the work done and made sure that their conditions were satisfied. i would also never submit a dishonest form saying 100% of the wall was insulated when it wasn't. i worked out the area and it was about 55% which was put on the form. just to clarify it is the home owner who fills out (and submits) the declaration of works form, there are 2 or 3 boxes for the contractor but it is the responsability of the homeowner to ensure the information is correct.
at the time i got the grant approval (early april/may) there was plenty of confusion between SEI and the contractors, with conflicting reports about what was possible with the grant and partial insulation. since then they have published a revised policy on partial insulation which is much stricter than originally advertised. however i believe they will honour the grant as they said they would. this is based on implementing complete wall insulation for the house, on the form i said i would be dry-lining the remaining walls at my own expense, and this was one of the conditions they said, as long as the entire house was being insulated that was fine, and that i would only qualify for grant assistance for one type of wall insulation. i also noted on the form that it would disturb the line of the terrace to insulate the front and back of the house at 120mm.
it's possible i'll be insulating the front and back externally anyway but either way i will not be dishonouring my side of the bargain with SEI.

i think you may need to contact sei to clarify the issue.i had a client a few months ago who wanted to do exactly the same as yourself and was told by the sei in writing that they would only receive the grant for the completion of insulation and a gurantee to insulate the remaining walls later be it inside or outside will not be sufficient.
it will come as a surprise to me if you get your grant which i hope you do,but just be aware the conditions for grants have not changed from day one, they have just been clarified.

sas

PCPL wrote: »

Also a point on the PIR insulation being unstable, was it not the kingspan K5 board which was found to be unstable? I stand to be corrected on this

The phenolic board was dropped.