Insulation for new house build

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#1465325 7-Jan-2016 18:58

I built a house 4 years ago, in ChCh, and have polished concrete floors with hydronic underfloor heating. Would definitely do it again if I built again. I have a 200mm thick slab to give extra thermal mass and it makes a huge difference, in both winter and summer. In winter (as suggested previously) I only run my underfloor heatpump from 9pm till 7am (cheap electricity). The slab takes a day or two to warm up when I first fire it up but after that it is only during the depths of winter that it runs for the full 10 hours. In the shoulder seasons it will usually shut off between 1-4am (there is a temp probe in the slab). The house hardly ever drops below 20 degrees, never below 18.

In summer the slab seems to absorb a lot of heat meaning our living room which has huge bi-folds, NW facing, never really overheats. And once the sun goes down and it starts cooling down outside, the slab starts releasing all the heat that has been stored during the day and it is lovely and warm inside.

I work from home and walk around in bare feet all year round. The concrete is a lovely warm temp in winter, and refreshingly cool in summer. Thermal mass is such an important consideration IMO. It can really make a huge difference to the comfort levels in your home. It basically acts as a big buffer, and is an excellent way to store heat when electricity is cheap in winter.

As already mentioned, insulation is also key to this. In particular slab-edge insulation, and not making any holes in your thermal envelope - i.e. downlights in the ceiling etc. Definitely worth spending a bit of time getting this right, it can make a huge difference to the enjoyment of living in your home IMO.

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#1465354 7-Jan-2016 19:37

@SumnerBoy how do you think the slab would be without the hydronic underfloor heating?

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#1465358 7-Jan-2016 19:44

Freezing! There are a few spots around my place with no pipes in the slab, I.e in the pantry, and the concrete in there is noticeably colder in winter.

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#1465452 7-Jan-2016 21:58

If you hate yourself and the future generations that will live in your house, put no underfloor heating in a concrete floor.

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#1465454 7-Jan-2016 22:10

1eStar: If you hate yourself and the future generations that will live in your house, put no underfloor heating in a concrete floor.

What if you didn't have a concrete floor?

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#1465464 7-Jan-2016 22:38

You wooden channel your hate in such a constructive manner.

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#1465569 8-Jan-2016 08:15

timmmay:
mattwnz: I was speaking to a builder/ developer who builds eco houses, and he advised against PVC from his own experience. He said they just don't stack up compared to the new aluminum profiles you can now get. Also questions over low term durability with the NZ conditions. Also many people don't like the look of PVC, they have a bit of a stigma to them. They are used a lot in the UK, and don't look great when retrofitted into terraces . I would suggest visiting some house that have had them in for the last 10 years to see how they are performing, and how the owners find them. With aluminum, they are a known quantity, and durable/low maintenance. I have some anodized ones that were install 12 years ago, and they look as good as new.

That's what many people say, but there's never anything to back it up, and it's not what the research I've found suggests. I already have french doors, another door, and a bathroom window in PVC, the oldest only a few years old but seems as good as new.

I agree with timmmay. I lived in a house in the UK close to the sea that had PVC retrofitted many years ago and it looked pretty good to me. I have just seen a PVC window frames that look exactly like wooden window frames, I wasn't able to tell the difference until the owner pointed it out. Some people keep going on about NZ conditions, are these conditions that much harsher than Scandinavia or other Northern European nations?

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#1465572 8-Jan-2016 08:25

Every kind of material have lasting quality version and crap out in a few years version. The wisdom is to choose the lasting version. Some PVC can last, some won't. Same with alloy. Eventually the metal will give up. One would think the best alloy should outlast the best PVC ... ? But finding the best is impossible unless you have a time machine?

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#1465579 8-Jan-2016 08:37

Most of my PVC is from thermalframe, sourced I believe from Germany, where they have plenty of experience with the material. I go with the white PVC, not the wood grain. The main downside is there are generally only those two colors, maybe one more wood grain color.

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#1465583 8-Jan-2016 08:44

mattwnz:I was speaking to a builder/ developer who builds eco houses, and he advised against PVC from his own experience. He said they just don't stack up compared to the new aluminum profiles you can now get. Also questions over low term durability with the NZ conditions. Also many people don't like the look of PVC, they have a bit of a stigma to them. They are used a lot in the UK, and don't look great when retrofitted into terraces . I would suggest visiting some house that have had them in for the last 10 years to see how they are performing, and how the owners find them. With aluminum, they are a known quantity, and durable/low maintenance. I have some anodized ones that were install 12 years ago, and they look as good as new.

Yeap they use them a lot here in the UK you're correct about the ugly thing. They look cheap and nasty, especially the fake wood grain PVC windows. The corner joins are also a bit rubbish looking where they use what looks like no more gaps to join the PVC.

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#1465602 8-Jan-2016 08:58

lxsw20: Yeap they use them a lot here in the UK you're correct about the ugly thing. They look cheap and nasty, especially the fake wood grain PVC windows. The corner joins are also a bit rubbish looking where they use what looks like no more gaps to join the PVC.

There are different ways of doing the corners. Some are plastic welded.

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#1465692 8-Jan-2016 10:22

SumnerBoy: I built a house 4 years ago, in ChCh, and have polished concrete floors with hydronic underfloor heating. Would definitely do it again if I built again. I have a 200mm thick slab to give extra thermal mass and it makes a huge difference, in both winter and summer. In winter (as suggested previously) I only run my underfloor heatpump from 9pm till 7am (cheap electricity). The slab takes a day or two to warm up when I first fire it up but after that it is only during the depths of winter that it runs for the full 10 hours. In the shoulder seasons it will usually shut off between 1-4am (there is a temp probe in the slab). The house hardly ever drops below 20 degrees, never below 18.

In summer the slab seems to absorb a lot of heat meaning our living room which has huge bi-folds, NW facing, never really overheats. And once the sun goes down and it starts cooling down outside, the slab starts releasing all the heat that has been stored during the day and it is lovely and warm inside.

I work from home and walk around in bare feet all year round. The concrete is a lovely warm temp in winter, and refreshingly cool in summer. Thermal mass is such an important consideration IMO. It can really make a huge difference to the comfort levels in your home. It basically acts as a big buffer, and is an excellent way to store heat when electricity is cheap in winter.

As already mentioned, insulation is also key to this. In particular slab-edge insulation, and not making any holes in your thermal envelope - i.e. downlights in the ceiling etc. Definitely worth spending a bit of time getting this right, it can make a huge difference to the enjoyment of living in your home IMO.

Thanks for the comments - what insulation did you go for under-slab and edge? Presumably rib-raft? Expol-X for the edge? Do you know approximately how much more a 200mm slab cost you over the standard? And if you did go rib-raft, did you go 200mm in your slab to mitigate thermal bridging?

I think our scenarios may be different though - I'm assuming from your post that your whole house is polished concrete? I'm only talking about a kitchen/living room/foyer, so it's probably only 70 m2, and I'm not worried about it being toasty enough in winter to walk around in bare feet. I totally get hydronic heating for whole house, as it's eminently sensible, but I struggle with the cost for the benefit of 1/3 of the house. As mentioned, my primary interest in concrete is for the aesthetic aspect, followed by easy cleaning etc.

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#1465725 8-Jan-2016 11:06

Not sure who had the brilliant idea to use aluminium in a window frame. Our house here in NZ which has those and they are like ice blocks in winter. Always freezing cold. Not sure if newer versions are any better, but if I ever sell this place, the first thing I look for in a house is windows without aluminium frames. I would even prefer older wood frames instead of aluminium.

I am from Germany and we use PVC windows. We had double glazed PVC windows in our German apartment for 15 years. No problems what so ever and they worked like they did on the first day. They where later replaced by triple glazed noise cancelling windows, because of increasing air traffic in the area. They are brilliant, simply because they have 3 states they can be in. Open in an angle to the inside, fully open like a door and closed.

There is a company in Christchurch that does German like PVC windows. The owner is also German I believe.

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#1465728 8-Jan-2016 11:08

I had a standard slab, not rib-raft. 50mm poly underneath since there isn't much heat loss down - heat rises after all ;). As for edge insulation I found it very difficult getting a design that would be signed off by the engineer/council/builder etc. So in the end made my ground floor framing 140mm (instead of 90mm) and hung the bottom plate over the edge of the slab by 25mm. Then we wrapped the whole building in 7mm ply (post-earthquake this seemed like a good idea!) and hung that 50mm below the bottom of the bottom plate. So I ended up with a 25mm cavity between the slab edge and my ply wrap, and into that I cut strips of 20mm high density poly and fed them in.

Not the most ideal solution but the only one I could come up with at the time. Oh yeah, I also wrapped the poly strips in silver building paper to give it some extra insulation properties!

Presumably you will have a slab throughout your house tho? Even if only a small percentage is exposed? Underfloor heating will still work in areas which are not exposed, just not quite as effectively. My old man had an EQ rebuild and put oak flooring over his concrete slab, with underfloor heating, and he finds it great and very warm.

YMMV.

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#1465730 8-Jan-2016 11:13

Has anyone used or considered using spray foam insulation? http://www.nzfoam.co.nz/

This is not the stuff that is sprayed in through holes drilled in the outside cladding.

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