Preferred wall build type for Passive House

just do it

As it says in the title, what would your preferred wall build-up by a new build to passiv haus standard?

Do-more

I'm about to build with twin wall timber frame but wonder if a better choice may well be to build with ICF with a 175mm inner layer of mineral wool and a insulated 70mm stud. The first floor could be concrete and air tightness detailing would be more straight forward?

sas

Do-more wrote: »

I'm about to build with twin wall timber frame but wonder if a better choice may well be to build with ICF with a 175mm inner layer of mineral wool and a insulated 70mm stud. The first floor could be concrete and air tightness detailing would be more straight forward?

You'll have a bloody great big cold bridge where your middle floor breaks the 175mm of mineral wool and the service cavity.

Double stud still sounds more practical.

Do-more

sas wrote: »

You'll have a bloody great big cold bridge where your middle floor breaks the 175mm of mineral wool and the service cavity.

Double stud still sounds more practical.

Very true if it's a two storey, but can be dealt with if you go for a timber first floor rather than concrete.

If it's a dormer you could also surely come up with a detail to address the cold bridge of the concrete first floor with insulation under the eaves?

sas

Do-more wrote: »

Very true if it's a two storey, but can be dealt with if you go for a timber first floor rather than concrete.

If it's a dormer you could also surely come up with a detail to address the cold bridge of the concrete first floor with insulation under the eaves?

I had figured the reason you were interested in ICF was for the concrete floor. Otherwise I don't think it offers you mucy given that you seem to be trying to upgrade it using TF techniques anyway.

There are PH ICF systems that'll get you down as low energy as you need. If ICF why not one of these?

Given where you're building I'd have assumed that TF was the most practical.

Poor Uncle Tom

For the ICF to be considered, all elements would have to be considered, including the ICF roof option (which doesn't include concrete) but is used in conjunction with the ICF walls, etc.

Anyway, if the house is going to be truly passive wouldn't the use of polystyrenes, concrete, galvanised metals and uPVC have to be taken into account? or are these only considered for low carbon or carbon neutral housing?
After all, the passive philosophy is as much about saving natural resources as much as the ultimate running cost of the end product? or am I wrong?

Getting back on topic, wasn't there a widely publicised passive house constructed in the ICF format recently.

sas

Poor Uncle Tom wrote: »

For the ICF to be considered, all elements would have to be considered, including the ICF roof option (which doesn't include concrete) but is used in conjunction with the ICF walls, etc.

I don't see the logic in this. The ICF roof options are not required to build with ICF to PH level. A regular house can have an ICF roof. You simply select your prefered construction option for any element and detail the junction between them (e.g. wall and roof) so that you satisfy the requirements of your design specific PHPP calcs.

Poor Uncle Tom wrote: »

Anyway, if the house is going to be truly passive wouldn't the use of polystyrenes, concrete, galvanised metals and uPVC have to be taken into account? or are these only considered for low carbon or carbon neutral housing?

Define "truly passive". I would define it as "PHI certified" and that doesn't take materials into account at all. They only guidance I ever got from them regarding materials was to use as many locally sourced items as possible. This has more to do with them promoting the PH concept however because the average joe isn't interested in importing building elements.

Poor Uncle Tom wrote: »

After all, the passive philosophy is as much about saving natural resources as much as the ultimate running cost of the end product? or am I wrong?

The philisophy may be, the certification isn't however afaik.

Poor Uncle Tom wrote: »

Getting back on topic, wasn't there a widely publicised passive house constructed in the ICF format recently.

There is only 1 certified ICF house in Ireland that I'm aware of and it was built using a german ICF system. It's near Newbridge.

There was some noise made by an Irish company that claimed to have achieved "passive levels". I spoke to them a couple of years ago and at that time they were doing likewise but couldn't offer a wall u-value below 0.18 if I remember correctly. A quick review of their website just now suggests that they can go to 0.1. However, at the time I spoke to them they didn't have the molds to create the better u-value wall components evem though they were advertising them.

Poor Uncle Tom

Thank you for clearing that up for me.

sas

I'm currently building passive with masonry and EWI.

My preference is for timber frame. However my preference had to be put to 1 side because price wise the masonry option is cheaper.

This was based on my personal stance that you can't use plastic insulants with TF. Also I favour cellulose and softboard for my insulation in a TF. Softboard is expensive by anyones standards. Finally I would need a rendered finish and I would want a ventilated cavity which means I'd have to use cement board to clad the outside. This too is very expensive.

At the time I started the TF option was approx 40k more expensive with a cold roof than the masonry EWI option with a warm roof. That was ultimately why I went the route I chose.

Once we're in for 12 - 18 months and the house has dried out etc., I may change my opinion. For now though I'd go TF purely from a quality view point.

If I was on a budget (which I would be), I'd go wide cavity.

I read the poll to be about what you'd chose if you could have any option i.e. not considering price.

just do it

sas wrote: »

For now though I'd go TF purely from a quality view point.

Why do you feel this would be better if you were confident of good workmanship being used on other options?

sas wrote: »

If I was on a budget (which I would be), I'd go wide cavity.

Yeah I suppose I should have said budget and an exposed western coastline site are the two main considerations for me. I'm vering towards full fill wide cavity as standard block built with 100mm cavity is the only house type around here. (And any new builds I see are still this!) Wide cavity is asking lads to modify what they're used to doing, rather than embarking on a new build type.

sas wrote: »

I read the poll to be about what you'd chose if you could have any option i.e. not considering price.

That was the intention. I've been reading about the pluses and minuses of the various systems for long enough now and felt a poll would be interesting to see how regular contributors feel when it comes to having to state a preferred option.

And so it is - pretty even stevens between wide cavity, EWI and TF at the moment.

Do-more

It's just the thoughts of all the work taping around the joists that is putting me off the TF! I'm doing it myself as labour is ridiculously expensive here. I've a feeling it's going to be painful to the arms and the brain.

I was in a house here nearing completion built with Swedish produced ICF's a few weeks back, they mentioned they had priced German ICF's that would have got them to certified levels but they said the cost was eye watering so went with the local ones and settled for 22kW/m2/a.

Hard to compare as they are building a single storey funkis using a contractor against my dormer with direct labour but their price per sq metre is roughly 50% higher than what I am budgeting.

I haven't priced ICF's for my build and won't but figured that with the cheapest ICF's supplemented with a inner leaf of mineral wool and timber it's a wall construction I could do almost all the labour on myself so might be more economical.

sas

just do it wrote: »

Why do you feel this would be better if you were confident of good workmanship being used on other options?

Of all the trades I've had exposure to, Carpenters have the biggest onus of accuracy on them. I would put this down to alot of their work being exposed i.e. on show.

I found 1 TF company that do outstanding work. It was the biggest disappointment on this build that I couldn't go with them. It wasn't even their fault, the TF quote was very good. The other items were what drove up the price.

I watched my roof build up on site using the spec I wanted for TF i.e. 80mm softboard and then 270mm cellulose. It was reassuring to watch it build up. I know that every inch of that roof is insulated properly as it stands.

Blockwork and concrete is dirty and needs to dry, can't be poured if it's too wet or too cold. A bloody nuisance basically. We had to wait 3 months the winter before last in order to get a day where we were guaranteed to get the correct temps to pour. Granted it was an extreme winter but it did happen.

The idea of having a building up and weather tight within a fortnight (assuming windows are ordered to allow for this) is nigh on impossible to dismiss.

However, given the conditions you've described, I wouldn't be as confident of TF at that specific location. I'd need to do more research.....

sas

Do-more wrote: »

It's just the thoughts of all the work taping around the joists that is putting me off the TF! I'm doing it myself as labour is ridiculously expensive here. I've a feeling it's going to be painful to the arms and the brain.

To clarify, you're talking about the floor joists for upstairs? Can you knock up a sketch of what you believe the junction is likely to be if you went for TF? The TF companies here don't tape around every joist in the floors, there are other options as I understand it.

I'd assumed that type of labour would be relatively common\affordable there. You learn something new everyday.

Do-more wrote: »

I was in a house here nearing completion built with Swedish produced ICF's a few weeks back, they mentioned they had priced German ICF's that would have got them to certified levels but they said the cost was eye watering so went with the local ones and settled for 22kW/m2/a.

The cost for the PHI certified systems is outrageous alright.

Do-more wrote: »

I haven't priced ICF's for my build and won't but figured that with the cheapest ICF's supplemented with a inner leaf of mineral wool and timber it's a wall construction I could do almost all the labour on myself so might be more economical.

What about the 2/3 rule of thumb regarding the vapour layer though. In ICF the concrete core is the vapour and airtightness layer combined. If you keep adding insulation on the inside, you'll easily end up with more than 1/3 of your insulation inside the vapour layer. This would result in moisture build up inside your wall and the potential problems that go with it.

Granted I may have miss understood you so this may not be relevant.

Do-more

sas wrote: »

To clarify, you're talking about the floor joists for upstairs?

Correct.

sas wrote: »

Can you knock up a sketch of what you believe the junction is likely to be if you went for TF? The TF companies here don't tape around every joist in the floors, there are other options as I understand it.

I've just had a look through what documentation I have and there is no mention of this detailing. I just know that I will install the inner layer of 175mm rockwool onsite which then gets the airtightness layer over it before the 70mm service cavity stud. I'm just assuming that to meet the airtightness layer from the roof I will have to carry the membrane up through the 1st. floor joists which will mean taping around every one. I'll email my supplier to check.

sas wrote: »

I'd assumed that type of labour would be relatively common\affordable there. You learn something new everyday.

Take home pay is not high but taxes and social insurance are considerably higher than in Ireland so the actual cost of employing subbies is very high. I'm told that I should budget for about €50 an hour for labour.

Was talking to a relative of the wife yesterday who is starting to build at present and when planning his layout the electrical contractor told him to estimate on €90 for each downlighter. :eek:

Carlow52

just on this:

one detail I have seen on this is to put a full depth noggin say 6" from the support, ideally in a straight line using hangers.

This provides an edge to tape the A/T layer to on top and bottom and makes the rest of it easier.

dealing with the end ones that are // to wals need a bit more care and attention