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(Near) passivhaus - next steps?


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Our architect is currently doing what we hope are the final tweaks to our design (which is in a  thread in the new design section if it’s relevant). We didn’t set out to build a passivhaus but as we’ve progressed and read more of this forum, a low energy house which uses passivhaus principles (good insulation, airtightness etc) has become more and more appealing. Or a passivhaus if it’s achievable. 

 

We also set out perhaps naively thinking that masonry was the obvious way to build as that’s what the majority do but we’re starting to like the idea of using ICF. Still undecided though. Research ongoing. 
 

I’m not sure our architect has that much (if any) experience of designing to passivhaus or near passivhaus standards of airtightness etc or ICF. 
 

What would you suggest in terms of approach?

 

I’ve seen references to PHPP. Should we be going to someone who can help us with this? 
 

I presume we need to find a structural engineer with experience of ICF or passivhaus? Or both? Which is more important if they don’t have experience of both? 
 

Anything else we should be thinking about?
 

If we went ahead with our architect and try to design a low energy and/or ICF house, I’m not sure we’ll end up with exactly what we need without it being a painful process. 

Edited by Selfbuildnewbie
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It's all about the detail. Eliminating cold bridges, wind tight and airtight junctions etc 

 

There's a lot more to the passive House standard, you need to look very carefully at window sizes and orientation, the orientation and shape / complexity of the structire. .this should be the job of the architect as needs to be designed in from the very start. You can of course just increase the amount of insualtion and get 90% of the way there... I don't know how feasible it would be to get another designer involved in something that's already designed.

 

An SE won't generally know or care about the standards as it's a separate part of the design. Regarding an engineer with ICF experience, not needed. And ICF house is just a nomael reinforced concrete structure and every SE in the land should know how to work with that....

 

I can highly recommend ICF. There's just less to worry about. Cold bridges are largely eliminated (or can be) and airtightness is simple. As we did was tape around the windows and wallplate junction. The whole house is just the right temperature, and it's super quiet, and feels solid 

 

We went for an extra 100mm insualtion on the outside (so 250mm in total). We're in the house 3 weeks now with just a couple fan heaters going and the house is a constant comfortable temperature. Go for it.

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8 hours ago, Selfbuildnewbie said:

I’ve seen references to PHPP. Should we be going to someone who can help us with this? 

If you want to build to PH standards then using PHPP is the easiest and correct way. I bought a copy back in 2009 when I was designing our house. It makes it very easy to alter single aspects of the build to see the overall effect on energy usage. It may seem overwhelming when first looked at but I read through the whole manual a couple of times before entering data. If you are accurate and methodical it's fine.

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3 hours ago, Conor said:

There's a lot more to the passive House standard, you need to look very carefully at window sizes and orientation, the orientation and shape / complexity of the structire. .this should be the job of the architect as needs to be designed in from the very start. 

Yep, we’ve come at it in reverse. It was only after a few people commented in the other thread that the form factor means it might be a PH that we started looking into it properly. South facing to the rear, and more or less a square, and simple elevations aside from a couple of dormers.

 

@Gone West, I’ll have a look thanks. Just wondered if there were people out there who know their stuff on this and could advise us, should it be too overwhelming (we’ve also got two newborns so not a lot of free time on our hands). 

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10 minutes ago, Selfbuildnewbie said:

Just wondered if there were people out there who know their stuff on this and could advise us, should it be too overwhelming (we’ve also got two newborns so not a lot of free time on our hands). 

there are consultants for anything you could want and PHPP is among them.

 

this might be a good place to start.

 

https://passivhaustrust.org.uk/members/map/

 

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Good places for info are the German passivhaus website, lots of good info freely available.

 

You can build a good building using any build method, the important bit is the contractor being good, because many will not read detailed notes and just do what they have always done, which may not be what you want.  The other thing is constructibility, so PIR in cavity may not be the way to go as it's too unforgiving.  A lower performance u value, may be better than a high performance u value badly installed.  So Rockwool or bonded beads etc.

 

Form factor makes a difference, but only in respect to how much insulation you have to add to meet the 10W/m2 criteria.  We followed the principles, getting rid of thermal bridges, continuity of insulation, high performance triple glazed, airtightness etc.  Our form factor is at the wrong end of the scale, long thin and single storey, all insulation at roof line.  But so far this heating season our gas input has equated to 13W/m2 (NE Scotland), that includes, a prolonged period of the boiler short cycling, drying the building out etc.  All in all pleased with the result.

 

Get the architect drawings and a highlighter. Get each cross section and starting at a piece of insulation, follow its path around the building, up the walls, roof, back down the wall and through the floor, your highlighted light should have no gaps.  Any gaps rectify.  Ask yourself could I install easily, example, our architect haf mineral wood and PIR insulation in the roof, I changed it, to counter battens (to increase fill depth) and full fill spray foam.

 

Good luck

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