Green Building Forum - Shape saves moneyâ€¦â€¦

Shape saves moneyâ€¦â€¦

ringi — Sun, 27 Nov 2016 18:00:01 +0000

NHBC has just published a report on how the shape of a building changes the energy usage.

â€œWhen the basic results from SAP are fed into the Buildings Regulations compliance methodology which follows, the benefits of Form Factor do not register. The current Building Regulations in the UK are therefore unable to provide an incentive for industry to design and build homes that have a more efficient type and shape.â€

See https://www.nhbcfoundation.org/wp-content/uploads/2016/10/NF-72-NHBC-Foundation_Shape-and-Form.pdf

Shape saves moneyâ€¦â€¦

joe90 — Sun, 27 Nov 2016 18:16:59 +0000

I remember reading similar many years ago, an oblong with the long side facing south was best, which is why I have used this shape.

Shape saves moneyâ€¦â€¦

barney — Sun, 27 Nov 2016 21:26:00 +0000

Geodesic dome, anyone

Barney

Shape saves moneyâ€¦â€¦

SteamyTea — Sun, 27 Nov 2016 21:33:28 +0000

I am sure we have discussed this all before.
Thing is, a house has to be usable and fit a plot.

Shape saves moneyâ€¦â€¦

gyrogear — Sun, 27 Nov 2016 21:42:42 +0000

http://www.domespace.com/en/home

one of these near me, maybe I ought to ask to visit !

gg

Shape saves moneyâ€¦â€¦

EasyBuilder — Mon, 28 Nov 2016 00:27:45 +0000

My god, is this why so many modern houses are like shoe boxes! I thought it was just for cheapness. What soul destroying blandness it creates. Adorned by cheap detailing to vainly try and hide the mind numbing uniformity. A simple rectangle is a castle keep, a blockhouse, a defensive shape that shouts out â€œgo awayâ€. A home should not do this! A home should welcome with open arms. An â€˜Lâ€™ or â€˜Hâ€™ or other complex shape, if well thought out, creates semi-enclosed outdoor spaces that are entry ways, sun traps, cooling shade, diffusers of sunlight into sunless rooms, and even more. To me a home should look more like this:

or this:

It should be a joy to look at, and a joy to live in.

As designers our challenge is not just to build the most efficient shape, but to build a shape that meets our other human needs as well. As always, to find the best compromise between conflicting needs.

Shape saves moneyâ€¦â€¦

ringi — Mon, 28 Nov 2016 09:04:04 +0000

You can put interesting shapes outside of the thermal envelope, and use different wall surfaces to make the building look interesting. You can have as many roof overhands as you like without increasing the thermal surface.

Some of the examples in the report are 100 times better then most new builds in how they look.

Shape saves moneyâ€¦â€¦

Ed Davies — Mon, 28 Nov 2016 10:17:50 +0000

Posted By: gyrogear: http://www.domespace.com/en/home

Yeah, but what if the altimeter software goes wrong and releases the parachute and backshell too soon before landing?

Shape saves moneyâ€¦â€¦

fostertom — Mon, 28 Nov 2016 11:11:41 +0000

Posted By: EasyBuilderAs designers our challenge is not just to build the most efficient shape, but to build a shape that meets our other human needs as well. As always, to find the best compromise between conflicting needs.

To even begin that, you have to understand the effects at all levels, to balance them ('compromise' is a dirty, politician's word - good designers do 'synthesis', which is quite different). By all means, go off-cuboid, but most designers don't understand the energy consequences.

Shape saves moneyâ€¦â€¦

joe90 — Mon, 28 Nov 2016 11:33:42 +0000

Well, I have designed a "shoebox" , it's a cottage with character that fits the local vernacular. It's also exactly what we wanted. There was no compromise at all. ( once we won our planning appeal!) . It would not win grand design house of the year but I am not worried about that.

Shape saves moneyâ€¦â€¦

adi — Mon, 28 Nov 2016 12:01:43 +0000

Energy loss is normally related to surface area so from a practical point of view a square box gives you the most usable space (volume) for a given surface area.

However a sphere is the most efficient and actually has the greatest volume for the least surface area but not very useful when it comes to building usable spaces;)

Shape saves moneyâ€¦â€¦

fostertom — Mon, 28 Nov 2016 13:57:18 +0000

Posted By: adia sphere is the most efficient and actually has the greatest volume for the least surface area

Except it's not exactly volume we're after - it's useable floor area, which needs to maintain its headroom right across, to be useable. Hence the optimum is a sphere with vertical sides aka a cube!

And if balancing solar gain against surface-area loss,

Posted By: joe90an oblong with the long side facing south was best, which is why I have used this shape

Shape saves moneyâ€¦â€¦

barney — Mon, 28 Nov 2016 14:10:42 +0000

Well actually a cylinder Tom ?

Bit like the dome building linked to above

Regards

Barney

Shape saves moneyâ€¦â€¦

fostertom — Mon, 28 Nov 2016 16:01:36 +0000

Posted By: barneyWell actually a cylinder Tom ?

True

Shape saves moneyâ€¦â€¦

ringi — Mon, 28 Nov 2016 16:02:05 +0000

Posted By: adiEnergy loss is normally related to surface area so from a practical point of view a square box gives you the most usable space (volume) for a given surface area.

It tends not to, as you have more wasted space with hallways etc, then you do with a "shoebox" shape, there is also the issue of how far you want the back of rooms to be from windows.

Shape saves moneyâ€¦â€¦

ringi — Mon, 28 Nov 2016 16:03:36 +0000

"Best" is clearly flats and with modem standards of sound insinuation they can be reasonable to live in.

Shape saves moneyâ€¦â€¦

skyewright — Mon, 28 Nov 2016 17:20:08 +0000

Combining

Posted By: joe90an oblong with the long side facing south was best

and

Posted By: barneyWell actually a cylinder Tom ?

If it's half a cylinder you are thinking of then maybe Nissen (of hut fame[1]) was onto something?

[1] https://en.wikipedia.org/wiki/Nissen_hut

Shape saves moneyâ€¦â€¦

gyrogear — Mon, 28 Nov 2016 19:02:07 +0000

Posted By: Ed DaviesYeah, but what if the altimeter software goes wrong and releases the parachute and backshell too soon before landing?

well, no doubt in that case, somebody would get... a Rocket...

Otherwise, I guess the Cx would be very low for our windy climes...

and if it ever *did* get blown out to sea, at least it would float...

gg

Shape saves moneyâ€¦â€¦

djh — Mon, 28 Nov 2016 20:19:13 +0000

Just to point out that while minimising surface area is one aspect of good energetic design, there are also other criteria, including for example solar gains. In our case it turned out that the most critical aspect was reducing the area of north-facing windows rather than the area of the south-facing ones or even the shape of the house..

Shape saves moneyâ€¦â€¦

ringi — Mon, 28 Nov 2016 21:29:45 +0000

As you increase the level of insulation solar gain become less useful, but north facing windows are always bad.
Remember your walls have such a low U value that increasing the area does not make much of a difference. However if building to Part L, wall area makes a great difference.

Shape saves moneyâ€¦â€¦

joe90 — Mon, 28 Nov 2016 22:41:13 +0000

However, with well insulated walls and adequate south windows the solar gain into the floors etc is useful as the solar gain stays within the envelope ( well I hope so as that's a principle of my build.ðŸ¤“)

Shape saves moneyâ€¦â€¦

DarylP — Tue, 29 Nov 2016 08:44:14 +0000

@ringi, I would suggest just the opposite..... as U-values fall/insulation levels rise, solar gain contributes a greater % of the (lower) heat demand.
Part L compliance takes no account of wall area, it uses the same shape for the notional/reference design.
Cheers

Shape saves moneyâ€¦â€¦

Ed Davies — Tue, 29 Nov 2016 09:03:10 +0000

Posted By: DarylPPart L compliance takes no account of wall area, it uses the same shape for the notional/reference design.

Could you clarify what you mean by â€œsameâ€ there? Do you mean that it always uses the same shape for the notional design (what shape?) or that it uses the same shape as the designed house?

Building regs airtightness effectively uses the designed shape: it's mÂ³/mÂ²/h where that takes the mÂ² as the outside surface area of the house so a house with a complicated shape is allowed to leak more overall.

Shape saves moneyâ€¦â€¦

ringi — Tue, 29 Nov 2016 09:20:42 +0000

Part L starts with the house shame and then works out the energy usage based on standard U values for wall, roof, floor, windows, assuming 20% window, etc based on that shape, this gives the required maximum energy usage.

The designed house has to have an energy usage no more than the required maximum energy usage, but for example you can trade off better walls so as to have more windows.

(Building regs control how the house is built, the same of the house is control by planning regs, yet planning regs don't care about energy usage.)

Shape saves moneyâ€¦â€¦

cjard — Tue, 29 Nov 2016 09:47:44 +0000

Posted By: ringi"Best" is clearly flats and with modem standards of sound insinuation they can be reasonable to live in.

I think your definition of "best" is too narrow here; high population density brings with it all sorts of downsides

Shape saves moneyâ€¦â€¦

cjard — Tue, 29 Nov 2016 09:49:41 +0000

Posted By: ringiif building to Part L, wall area makes a great difference.

Given that Part L and Passivhaus spec are now aligned with regards to insulation levels on walls, I'm inclined to disagree with this

Shape saves moneyâ€¦â€¦

ringi — Tue, 29 Nov 2016 09:58:31 +0000

Posted By: DarylPI would suggest just the opposite..... as U-values fall/insulation levels rise, solar gain contributes a greater % of the (lower) heat demand.

Posted By: joe90However, with well insulated walls and adequate south windows the solar gain into the floors etc is useful as the solar gain stays within the envelope ( well I hope so as that's a principle of my build.

Most solar gain is in the summer were no houses in the UK needs heating, letâ€™s discount this.

The next highest months of solar gain are in the spring and autumn.

Even a house build to Part L standards is unlikely to benefit from much solar gain at the start of the autumn, as it is gaining more energy from the people living there and electrical items, then it is losing.

As we get closer to passive home level, the house does not need solar gain in the autumn, it also does not need solar gain towards the end of the spring. There is very limited solar gain to be had in winter, due to the lengths of days and how little sun light gets to the earth even in the day time.

Hence energy modelling needs to be done on â€œday by dayâ€ bases using data from a few years, not looking at average heat requirements and solar gains.

I expect that in â€œreal lifeâ€ most homes donâ€™t have much option for solar gain based design, as homes are put on both sides of roads, and road layout tend to be decided based on the shape of the land. Even avoiding windows on the north side of a house can be hard as people like windows to look over their garden.

Shape saves moneyâ€¦â€¦

Greenfish — Tue, 29 Nov 2016 10:18:56 +0000

My house is an "interesting shape", and I wish is was a box. We have insulated well, but just about every room has 3 external walls, and it is 1.5 storey too, so inner walls that become outer, lots of wall per floor/roof area and inevitabley more heat loss than the same area in a simple 2 storey box.

But we had no choice (other than not build anything). It is a sensitive site, the architect and original owner negotiated this silly shape with the planners, and it was the only thing they would accept. We looked at getting a variation to the pp, but the council said no, so we built what we were permitted. To me this is crazy, and I look forward to the day when planning encourages if not enforces energy efficient shaped buildings.

Shape saves moneyâ€¦â€¦

ringi — Tue, 29 Nov 2016 10:54:03 +0000

Could you use permitted development to "fill in" with some extensions.....

Shape saves moneyâ€¦â€¦

SteamyTea — Tue, 29 Nov 2016 10:58:43 +0000

The solar gain issue is a lot more complicated than people think.
It is not the absolute value of the suns power that is the issue. It is a combination of the power and the angle that it hits the building.
There is also the air temperature to take into account, and the windspeed.
A low sun angle, on a clear day like today may have a greater impact on the internal temperature than a higher angle in the summer.