This is a cross post from the navitron forum.

I'm just about to submit a planning app on bungalow with room in roof (so 1+1/2 story?).

I have a layout (see below) that has been created after consultation with the architect and a planner.

The light blue sections are windows
Dark blue are entry/exit points like front door or patio doors(i.e. openings down to floor level)
The green rectangle shows the upstairs area

It is currently back with with the planner for comment. If he gives the nod we'll work up the full application an go for it (fingers crossed).

Assuming the planner say go:

The building is ~9.5m by ~13m, aligned with the long axis (13m one) North/South.

The overall height is 5.5m from floor level. The floor level will be just above local ground level (we will have to dig down but will dig down so that the new ground level is lower than the building floor level.

My budget is ~150k all in with me acting as the prime contractor.

As I am in a conservation area and an area of outstanding natural beauty the external look of the place will have to be "traditional" e.g clay tile roof (this has been specifically highlighted by the conservation officer) and render or brick exterior (i'd like to avoid brick on cost and personal taste grounds but am not dead against it if there is a compelling reason). That's not to say other external finishes like wood or metal are off limits, just we'd need a good reason for specifying them.

My question to the forum is:

WHAT SORT OF CONSTRUCTION SHOULD I GO FOR? I'm talking about foundation, wall and roof construction.

I have my theory on the best construction, but I won't post it yet as I'm interested in other people's ideas, this is really a brainstorm session so I can get lots of view points to help me make a decision.

and the navitron topic

http://www.navitron.org.uk/forum/index.php/topic,7774.0.html

Hi beelbeebub,

Hopefully there'll be some more comments along in a minute! (for anybody else, anything I write that's cryptic is probably to suggestions on the navitron forum)

Foundations: It all depends on the ground conditions, so you'll need to give more info. Even then you're probably best to rely on somebody who's familiar with the site. But be aware car tyres are very labour intensive!

Walls & Roof: When you say you will be prime contractor, do you mean you will be managing or labouring? If you're labouring, then pick a technique you feel comfortable with. I like straw but it will take more space than you've allowed for. Render seems the obvious choice for the external surface.

Design: without seeing the surrounding properties etc it's difficult to make any useful comments. I'd assumed from the high windows on both E and W that you were close to other properties on those sides, but I guess not if the road is N/S. Equally, the roof seems to be gable at the N and hip at the S, which is a bit odd and it's not clear why you didn't maximise the floor area and windows on the S?

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2844&Focus=36948#Comment_36948

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=931&Focus=10164#Comment_10164

try your own search for chalet bungalows and air tightness too.

Plenty of detailed guidance can be found here

http://www.planningportal.gov.uk/england/professionals/en/1115314255826.html

why not go better than passivhaus? the standard has been arround for quite a few years now.

exactly

When using sheet insulation great care must be taken not to have any gaps or cracks or air paths from in to outside, one of the worst things is service penetrations put in afterwards!

Hope all goes well.

Yes, the speed of SIPS is attractive.

The thermal mass question is still unresolved. My gut says a bit of mass is good, esp if my roof structure is v.low thermal mass.

Some of the arguments about modern usage patterns (i.e. out all day, so low mass for quick response on return) are compelling. My main thought is that a lightweight system requires some good control to prevent over and undershoots. A massy system has an easier job, a bit like the difference between driving a lorry and a sports car. Get it slightly wrong in the sports car and you're doing 100mph before you know it.

I'm also slightly iffy about the life of SIPS, it's not a hugely rational thing and I'm open to be convinced. I'm kind of aiming for a long life structure. Most of the buildings nearby are heading past 150years and still going strong. Sure they've had windows hacked through walls, been converted to flats, bedrooms have become kitchens, toilets, central heating, wiring, phones have all been added but the basic structure is still solid and should be good for another 150 by which time they'll have had the teleporter wired in, a fusion station in the basement and the roof will have been replaced by a force bubble or something.

I know SIPS have been used for 50 odd years but will they last another 100? esp with all the hacking/extending/converting that inevitably goes on as buildings encounter changing architectural and social fashions.

I'm not saying that SIPS won't last just that we don't know for sure that they will.

There are plenty of timber buildings lasting several hundred years but they all use discrete load paths, if a load bearing post or beam is in the way or damaged it's relatively easy to replace it or route the loads around it with more beams/posts. As the loads are transferred through the skin I can imagine that replacement or rework are difficult.

Carbon fibre structures use as similar strategy of stresses skin supported by lightweight monolithic foam. They are notorious for being dodgy when it comes to damage and the difficulty of repair and reworking.

cheaper to use one thickness of insulation eg 200mm

Hi,
They do do it at monster sizes but its less freely available.
This is similar to our local method except they dont do the external insulation so it is (ive missed out vapor layers etc).
This is what i have found ie struggled with (learnt) so may help somebody with thier own variant- its never as easy as it appears:
Block (laid flat = 225mm)
batten horizontal (plank)top/bottom/middle
insulation board
studding 50mm ( 2 x 2)
plasterboard
Ive done this with 100mm insulation and the problem are as follows
1) fixing thropugh 100mm of board is hard. There are screws (i used 6 x 130) to pick up on the solid wall you would need to use hex head rafter screws (eg from S/fix at 150mm+ length - these get pricey as are in packs of 20 not 200)
2) You have to be exact in marking where the batten is otherwise the the insulation mounting screws miss, hence using plank size wood to ensure a hit.
3) although the internal studding is fixed top and bottom at 50mm its still quite bendy(or is bent) so occaisionally you need a big fixing to go all the way through to support and get it back in line.
4) Kingspan/celotex is not flat - longways/cross ways = bowed bananas (need EU regulated straight bananas)and at 100 mm its is surprisingly strong and resistant to straightening. A screw head will pull through very easily. So you need to make ply washers ie 6mm ply about 2"x2" to clamp it onto the batten. If its too bowed then the stud frame is well off of the wall, this can be shimmed square of course.
5) you could lay further planks horizontally and clamp through the insulation into either the batten or the wall, but agin the max hammer fixing is about 130mm with only 30 penetration into the wall, and you have the framing that would be on top. This framing void is for services - I can do pipework with the 50mm gap.

The advantage of this method is that the insulation board runs top to bottom continuously. I have rebated and sealed it to the upstand of the floor slab perimeter insulation. The perimeter insulation is 50mm board, so i cut a 25 x 25 rebate along the top edge, then brought the wall insulation standing 25mm off of the solid wall down to sit atop the perimter upstand. Thats my home-made robust detail.
Likewise at the rafter level going cross-ways i cut strips of 6mm ply into 120 mm widths and fixed this to the underside of the joist up against the wall head sole plate, thus the insulation can then be sealed tight upagaintst the underside of the joist. Then from above i filled downwards between the joist to meet this ply. It was too difficult to cut and fix up the wall and threough the joist as a continuous run.

Hope this gives you food for thaught. I had to work this out myself as I went along. thats not too much of a problem, what got my goat was the derisory commnest form the builders - whats the point, thats not how we do it, its good enought way we do it etc etc.

Cheers

Mike up North

I dont think fixing one sheet to the next will either work or is a good plan.

To have good effect, insulation should be thought of as "Outsulation"(George Swanson, USA) thereby creating thermal mass internally out of any solid material. The idea that wanting to quickly heat a space on ones return from the day out is absurd if it is thought that this is only possible with a lightweight structure. In that instance, the internal air is being heated from fresh/cold. Is there more air in a 'heavy' building than a 'lightweight'? If we have outsulated thermal mass, surely there will be less requirement to heat on ones return? And what on earth do sheets of modern insulation do for humidity transfer, other than trap it? Air tightness polythene membranes.... great for one problem but introduce huge problems with breathability/humidity. Has anyone yet genuinely proved that timber kits can be properly recycled with all the glues and other nasty modern materials? To think about longevity too... think 50's scout huts, sagging, damp, rotting, cold.

Humm, as far as I can see, durisol is an Insulated Concrete Form system. The difference is that it uses a wood based form rather than a polystyrene or other plastic.

I looked at ICF but was turned away by the lack of internal thermal mass. They are a great Idea but the problem is that the thermal mass is locked up inside the insulation.

Given that the Durisol material is some type of mineralised wood (hence I suppose the insulation value from the porous nature) I wonder if they could vary the mix throughout the block so that there was dense concrete in the inner face changing to insulating for the outer face. That would be a very interesting product.

I'm a little confused by HarryLime, is he saying the vapour permeability of the PU sheets could be a problem? I have to admit that I have slight worries on that score. I would rather only have a single thin vapour barrier, but if I put a polythene sheet between the blockwork and the PU I could risk trapping moisture in the PU. Not there is a school of thought that says this is not a problem as PU is inert. If possible I would like not to trap water in my structure.

That brings me onto simply using taped PU bats as the vapour barrier, any ideas?

@ # breatheconstruction

But the porous wood cement bit must be low thermal conductivity as it goes from external face to internal face. If it had hight thermal conductivity it would act as a thermal bridge.

If it is a low thermal conductivity material then the internal face of it must act as a low thermal mass solid?

Thermal mass the specific heat capacity (SHC) i.e.the energy required to change the temperature of 1kg of by a given amount (usually 1K). But if that material has a low thermal conductivity then it doesn't matter what the specific heat capacity of the material is as it won't reach the surface very easily.

Conversely a material with high conductivity but low SHC would heat up and cool down too quickly.

If I had a house with 1m thick granite walls that were nicely heated to 20c then I opened the door and a cold 0c wind blew through, the granite surface would quickly cool down even though an inch below the surface the granite was still warm. In this case the thermal mass wsa unable to moderate the air temperature.

To act efficiently thermal mass must also be coupled with the correct thermal conductivity. Now I'm not sure quite what that balance is, maybe it is Durisol. But intuitively it seems that anything that is conductive enough to be a good thermal mass must be too conductive to be an insulator.

Does anyone have any explanations?

Have I got the wrong end of the stick?