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Author Topic: New house design stage  (Read 6582 times)
Greenbeast
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« on: September 19, 2017, 08:35:23 AM »

I've played the game of ideal house-build before, but now i'm looking at it for planning permission submission next year.
There's lots to tackle, my first two queries are so i can start to get a decent 3d plan together.
I'm looking to have a covered porch along the front (south-facing) elevation, to prevent over-insolation of the glazed portion during the hot summer months. Is there a calculator/method out there so that i can work out the ideal extension/height of the cover to get the best out of passive solar heating?

Not looked at building materials in a while. I think, although i would loved rammed earth, that's never going to pass muster with the boss, so i reckon we're looking at timber frame/SIPS, what sort of wall thickness should i be looking at. Want to get it right early on, insulation-wise, seems mental not to.
« Last Edit: September 19, 2017, 08:46:28 AM by Greenbeast » Logged
dhaslam
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« Reply #1 on: September 19, 2017, 09:15:48 AM »

I have an overhang of about one metre on the south side.   Midday sun is just coming into the rooms now which is about right.    East and west windows are the ones to be careful of because the sun comes shines directly in.     

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Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Greenbeast
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« Reply #2 on: September 19, 2017, 09:24:51 AM »

Thanks, whereabouts in the country are you? What sort of height is the overhang?

The west is shaded by trees, the east we'll have to watch, there is a tree-line but maybe not enough shade
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A.L.
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« Reply #3 on: September 19, 2017, 09:59:32 AM »

hello FWIW,

- for shading of south facing windows ideally draw two lines, one at ((90-latitude)-23.5) up from horizontal at lintel and one at ((90-latitude)+23.5) from windowsill. Where they intersect gives full exposure on Dec21 and no exposure on Jun21

- for a U-value of 0.12 with fibrous type insulation in a timber frame you are looking at a total thickness of 350mm for a render finish or perhaps 400mm for a rain-screen construction
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Fionn
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« Reply #4 on: September 19, 2017, 10:33:45 AM »

Dhaslam is spot on, it's definitely the East and West that are tricky to shade effectively. South is very easy.
Personally I'd go with PIR fill and a further PIR wrap outside if going timber frame, should reduce the wall thickness quite a bit over fibrous insulation and the insulation will actually help stiffen the wall a lot - not that anybody will include it in any calculations obviously.
Picking the rainscreen is the tricky bit!
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PV - 2.75kW East, 1.5kW South, 2.5kW West. 3 x Flat Plate Solar Thermal with side arm FPHE on 268L cylinder
dhaslam
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« Reply #5 on: September 19, 2017, 10:57:23 AM »

Thanks, whereabouts in the country are you? What sort of height is the overhang?


Latitude is 53 degrees Irish Midlands.   The  overhang supports the roof with pillars so shading starts at chute level.

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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Warble
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« Reply #6 on: September 19, 2017, 01:12:50 PM »

In a new house wall thickness is not so important so I would use an I-beam timber frame with fibre batt insulation. I wouldn't use PIR because it is expensive, highly combustible and not sustainable.
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todthedog
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« Reply #7 on: September 19, 2017, 02:47:24 PM »

Have a look at this GB

http://inhabitat.com/prefab-prispa-by-romanias-solar-decathlon-team-produces-20-more-energy-than-it-uses/

Not far off what Mrs T and I were looking at building a couple of years back.
I have contact details if wanted
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Fionn
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« Reply #8 on: September 19, 2017, 05:57:50 PM »

Here in Ireland people are obsessed with using traditional cavity wall construction using 4in blocks for the inner and outer leaf. They are using cavities up to 250mm now to get the desired u-value which leaves you with a wall a good half metre thick.
I think they look ridiculous myself to be honest, it's like going back to living in medieval castles.
I wouldn't be overly concerned with the flammability of PIR in a domestic setting. Given that it will be encased beind OSB on the outside and OSB + plasterboard inside, the house will be long gone before it goes on fire.
Grenfell a different kettle of fish entirely.
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djh
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« Reply #9 on: September 19, 2017, 10:17:43 PM »

- for shading of south facing windows ideally draw two lines, one at ((90-latitude)-23.5) up from horizontal at lintel and one at ((90-latitude)+23.5) from windowsill. Where they intersect gives full exposure on Dec21 and no exposure on Jun21

I agree with these sums but be aware that they may not help you much. I have two large windows on the ground floor that face south. The original design had a brise soleil across the top of them, but for various reasons it wasn't fitted. My plan changed to installing a pergola instead, with deciduous vegetation (i.e. grape vines) to provide shade. But I still haven't fitted that after two years. My problems are (1) in winter and up to sometime in April I want as much sun as possible; from later in April through the summer I would ideally have some shading, but my wife and I enjoy the warmth and only start to worry if it approaches 28C, so (2) working out the best position turns out to be a different problem than that solved by the equations. (3) Summer bypass on the MVHR is really important to helping temperature regulation, and I can't help thinking that some kind of adjustable external shading might be better than a brise soleil or pergola for the same reason - active control.

I have large roof overhangs (mainly to keep the straw bale walls drier) that shade the upstairs windows. The house was designed with PHPP to PH standard so our east and west facing windows are reasonably sized and the north facing one is lonely! East windows are not as bad for overheating as west ones, so you're in luck.

For design ideas for a south-facing enclosed porch, I'd suggest the best place to start might be to look at Hockerton.

I'm with warble - my walls are half a metre thick and I and others think they look good. Long before Grenfell I decided not to use PIR/PUR in my house because of the toxic smoke risk. I did use EPS underfloor and in the sun room outside the thermal envelope, and I would have used phenolic if necessary. I used mineral wool in internal walls and first floor void and some wood fibre around windows. But apart from straw bales my first choice insulation has to be cellulose, which we used for the roof. It's good acoustically and humidity-wise as well as helping airtightness and being easy to get installed.

I'd go with a good timber frame company rather than SIPs, myself.
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Cheers, Dave
Greenbeast
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« Reply #10 on: September 20, 2017, 07:33:11 AM »

Thank you very much for your thoughts Smiley
Lots to consider
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pdf27
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« Reply #11 on: September 20, 2017, 08:22:13 AM »

I'm going through the process of adding another storey to my house at the moment, aiming for the EnerPHit standard which essentially means that the upper storey is to PH standard and the lower storey is a bit compromised by the existing structure. A few thoughts so far:
  • Glazing orientation isn't that critical - we're mostly north facing (forced by the house) with no shading on the south orientation, and aren't having to work too hard to hit EnerPHit - and PHPP shows virtually no overheating risk. Don't concentrate on sorting the glazing orientation out at the expense of it working as a house.
  • Strong preference for cellulose-insulated timber frame here - total wall thickness ends up as about the same as blockwork/foam, but being that timber frame tends to be factory built that fits with our likely timescales (currently living in the house, want to minimise the time we're homeless.
  • It's questionable how much it's worth concentrating on the last little bit of performance, and whether overheating is really such a problem - for new build then heat pumps make a lot of sense, particularly if you have the room to go ground-source. That makes adding in cooling really, really cheap and even a little bit of extra heat in winter doesn't cost much. Have a think about your preferred balance of generation versus reduced consumption - particularly with heat pumps it isn't at all clear to me that dealing with overheating purely by house design is necessarily the right route. Even without active cooling PHPP has our house which is mostly North/South has virtually no overheating, with the insulation helping a lot here - shading to reduce this further would have a big visual and potentially cost impact, to deal with something that active cooling does better (e.g. providing overnight cooling when the outside air temperature is 30C for that one day a year/
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Greenbeast
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« Reply #12 on: September 20, 2017, 08:57:19 AM »

I'm going through the process of adding another storey to my house at the moment, aiming for the EnerPHit standard which essentially means that the upper storey is to PH standard and the lower storey is a bit compromised by the existing structure. A few thoughts so far:
  • Glazing orientation isn't that critical - we're mostly north facing (forced by the house) with no shading on the south orientation, and aren't having to work too hard to hit EnerPHit - and PHPP shows virtually no overheating risk. Don't concentrate on sorting the glazing orientation out at the expense of it working as a house.
  • Strong preference for cellulose-insulated timber frame here - total wall thickness ends up as about the same as blockwork/foam, but being that timber frame tends to be factory built that fits with our likely timescales (currently living in the house, want to minimise the time we're homeless.
  • It's questionable how much it's worth concentrating on the last little bit of performance, and whether overheating is really such a problem - for new build then heat pumps make a lot of sense, particularly if you have the room to go ground-source. That makes adding in cooling really, really cheap and even a little bit of extra heat in winter doesn't cost much. Have a think about your preferred balance of generation versus reduced consumption - particularly with heat pumps it isn't at all clear to me that dealing with overheating purely by house design is necessarily the right route. Even without active cooling PHPP has our house which is mostly North/South has virtually no overheating, with the insulation helping a lot here - shading to reduce this further would have a big visual and potentially cost impact, to deal with something that active cooling does better (e.g. providing overnight cooling when the outside air temperature is 30C for that one day a year/

Interesting thank you.

We do have plenty of space for gshp actually. I kinda hadn't considered it because my parents have not had the best time with it. Is it worth while (I really, really hope the house will have a good solar array)?
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Greenbeast
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« Reply #13 on: September 20, 2017, 09:03:01 AM »

re:GSHP, works better with UFH no?
Concerned about UFH because of the dogs, have always assumed i'd put it in a house i'd build until i met my g/f with her pack
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marshman
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« Reply #14 on: September 20, 2017, 09:04:19 AM »

As a bit of a "curved ball" what about a bit of Thermal Mass?    I am all for highly insulated, controlled ventilation etc. but in my experience you get a more stable and just as importantly "comfortable" atmosphere in a house if it has a bit (ok a lot) of thermal mass. Obviously this works better if the house is occupied 24/7. My thinking, (no actual hard facts or figures so please discuss/dismiss as you feel fit), is in the summer the thermal mass limits the day time temp rise whilst giving it up in the evenings, works well in the "shoulder" months. The building is incapable of sudden temperature changes, so after a cold frosty night in the winter the house is still warm in the morning.  The disadvantage of a lot of thermal mass is it can take several days to warm the house if you go a way for a few days, but now we have a GSHP running I just leave it "ticking over" 24/7.

The house we have is an old farmhouse with thick walls and a massive central brick chimney - admittedly you would not do a new build this way, but it is well insulated with an inner skin of 5" (125mm) thermal (celcon) blocks and a foam filled cavity. The external wall is 12 to 18" solid brick. It is a large house (over 200 m sq) yet the heating from the GSHP uses about 1800kWh of electric, per year (approx 7200kWh heat). We do have a woodburner in the north facing lounge which contributes a bit but not very much.

Just a thought.

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
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