Fundamentals: Timber frame cabin plans

1 to 28 of 28

- CommentAuthorstephendv
- CommentTimeJul 18th 2010
Back with some more sketches for the timber frame cabin I'm planning.
Base and wall detail: http://www.casanogaldelasbrujas.com/base_and_walls.jpeg
Roof detail: http://www.casanogaldelasbrujas.com/roof.jpg

Foundations will be 10 pillars which support a glulam base 200x320 and normal timber floor trusses 40x160. I've been pouring over american house building books so am not sure of the European or metric standard sizes for the twobaX's they keep mentioning. So a few questions:

- Instead of using OSB between floor trusses to hold the insulation in place, can I use EPS panels instead - two birds one stone?
- What are the standard sizes for truss hangers?
- According to american code 40x100 studs (2x4) have to be at 400mm centres - could I go to 600 for such a small building?
- To simplify the roof trusses, I plan to build the front wall higher than the rest, then join the ceiling rafters directly to the studs in the front wall, is this ok? Will I need blocking in the front wall or will the interior OSB sheathing be enough?
- Roofing will be 4m long metal panels, do I need any kind of moisture barrier underneath it? If so, can I lay the moisture barrier directly on the rafters?

Thoughts welcome
- CommentAuthortony
- CommentTimeJul 18th 2010
Glulam seems like a crazily expensive way to go and they introduce thermal bridging

EPS will support insulation but is not vermin proof which may be necessary?

In your plan you dont need truss hangers as you could use bearers, but truss hangers come in loads of sizes -- jiffy hangers would be cheaper.

You could go 600 c/c

no blocking needed unless engineer wants it. Ceiling tie 100 40 will need a hanger or the ceiling will bow down mid span, hang from roof rafter.

moisture barrier should go on top of plasterboard and cross battens to ceiling could be omitted.
- CommentAuthortony
- CommentTimeJul 18th 2010
I fancy insulated roof panels but they could be more expensivethought they could be the ceiling too.
- CommentAuthorstephendv
- CommentTimeJul 19th 2010
Thanks tony, local carpenter will supply glulam at 571Euro/m3 and standard timber at 442/m3. Seems OK to me. Will need something very strong for the base as it needs to span 4m and shouldn't flex if the house is ever lifted onto a truck.
Vermin might be a problem, very rural location, so I'd have to go OSB panel for support and then use rockwool all the way instead of EPS.
The interior moisture barrier will be the OSB with taped joints. Didn't want to perforate the OSB with light fittings, but since it's OSB it might be easy to seal.
- CommentAuthorchuckey
- CommentTimeJul 19th 2010
I may have missed the point but I can't see any roof insulation. I feel that the "metal" roof should be corrugated with out any "eave" filler, so the underneath of the metal can evaporate water. If you used the Corus insulated roofing sheets (coloured on top, thin steel,3" foam, thin steel, coated white PVC) like in your big box supermarket, the roof would go on quickly.
Frank
- CommentAuthorstephendv
- CommentTimeJul 19th 2010
Roof insulation will be rockwool on the ceiling. I've used the insulated metal sheeting for another little project and it was great to work with. Thought I would cut costs and go with just plain metal here since the insulation will be in the ceiling. Any reason to still use the insulated metal sheets?
- CommentAuthorstephendv
- CommentTimeJul 22nd 2010
Can anyone comment on the glulam and truss dimensions, and see if they're Ok?
- CommentAuthorJulian
- CommentTimeJul 23rd 2010
Stephen,
is this in Spain? If so aren't panel sizes 2,0 x 1,0? If they are why not keep it simple and go for 500mm stud centres?
- CommentAuthorstephendv
- CommentTimeJul 24th 2010 edited
Yep, in Spain, but panel widths for OSB and drywall are 1200 so I'm leaning towards tony's suggestion of 600 centres.
- CommentAuthorstephendv
- CommentTimeSep 10th 2010 edited
We've finished the foundation pillars and the glulam base, floor to go in this weekend. The glulams are 140mm wide which is plenty surface for 100mm stud with rockwool infill + EPS. Now the question is, should I put the EPS + PSB on the outside of the stud, or on the inside? (I know viking house likes the outside option).

Option 1 (inside to out):
Plasterboard directly on 100mm studs, services go through studs, OSB sealed with mastik silicon sealer to create vapour barrier, 40mm EPS, 20mm battons, reflective Tyvek style vapour barrier (is this necessary?), timber cladding.

Option 2:
Plasterboard directly onto EPS (services cut into EPS), OSB sealed to create vapour barrier, stud, Tyvek wrap, battons, cladding.
- glulambase.jpg
- CommentAuthorTimber
- CommentTimeSep 10th 2010
None of the above?

Option 3: (From inside out)
Plasterboard
500 Guage polythene vapour control layer sealed and lapped to create air tightness membrane (careful with service penetrations)
100 mm stud filled with mineral wool insulation
OSB sheathing
40 mm EPS
High performance breather membrane
Vertical cladding battens
Timber cladding.

Option 1 and 2 above (I suggest) might suffer from an interstitial condensation risk due to the lack of a vapour control layer on the WARM site of the insulation. OSB on the outside of the frame wonâ€™t do this.

Option 4 could also be considered
Plasterboard
25x50 mm vertical timber battens
Polythene vcl with all joints taped and lapped etc (this could be removed subject to an interstitial condensation risk check)
OSB also sealed at joints to make doubly good
100 mm stud with mineral wool insulation
40 mm EPS
High performance breather membrane
Vertical cladding battens
Timber cladding.

Timber
- CommentAuthorledger.123
- CommentTimeSep 10th 2010
what windows are you putting in, aluminium,timber or pvc
- CommentAuthorstephendv
- CommentTimeSep 10th 2010
Timber,

In option 1 I thought since the OSB would be behind 40mm of EPS it could be considered warm? You commented on the Option 2 design in a previous thread and said that it would be fine! See: http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=5961&page=1

Essentially option 1 is: 100mm rockwool, OSB VCL, 40mm EPS. Option 2 is just reversed: 40mm EPS, OSB VCL, 100mm rockwool.

I wanted to use unpunctured OSB as a VCL because working with a polythene sheet seems like a nightmare. Would it have to go under the floor too?
- CommentAuthorevan
- CommentTimeSep 10th 2010
Polythene vcl is dead easy to work with, just use a liberal amount of staples and make sure it overlaps across a batten so that the plasterboard or floorboard tightens down to seal it. I even used it to hold up 300+mm of glass wool in the ceiling before putting the plasterboard up.
- CommentAuthorstephendv
- CommentTimeSep 10th 2010
Windows will be timber.
- CommentAuthormarktime
- CommentTimeSep 10th 2010 edited
Stephen you might find this site interesting at this point in your build.

http://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers

For interest, I'm being offered the following by a local timber-frame supplier, (bear in mind that I'm in the sub-tropics).

plasterboard/ t& g pine
147 mm stud (un-filled)
30 mm EPS
3 mm channels cut into EPS
breathable membrane
12 mm fibre-cement board, taped and emulsion washed (i.e impermeable barrier)
mesh
cement-based plaster.
- CommentAuthorTimber
- CommentTimeSep 10th 2010
Stephen

It has 100 mm of mineral wool on the over side so is sort of in the middle, not on the warm warm side.

Plus OSB is vapour permiable, so won't be a vapour barrier.

Plus the breather membrane should be over the insulation, not directly behind the cladding. It can trap moisture where it touches the cladding and lead to decay. There needs to be a vented void for both the cladding and the timber frame structure.

My suggested option 3 or 4 is what I would do. I would probably, all things being equal, go with my option number 4. Best possible air tightness detail, lowest risk of interstitial condensation on anything critical etc.

Marktime - I am sure everyone will agree that 30 mm of EPS insulation is nowhere near enough!!! Plus the whole board over eps with groves in it sounds a bit risky to me.

Timber
- CommentAuthormarktime
- CommentTimeSep 10th 2010 edited
For sure I'm not suggesting fot one minute that this would be appropriate for northern Spain. I posted out of interest only. What is iinteresting is the vapour path design, i.e. no internal vapour check. The ribbed EPS was a bit puzzling to me too but I haven't spoken to anyone in a position to explain the reasoning behind it.

Calcs for my region are ext 17.9 deg C 66% RH ext and 20 deg C 55% RH int. Not what you would call challenging.

Where do you think the risks would lie?
- CommentAuthordavidfreeborough
- CommentTimeSep 11th 2010 edited
An internal polyethylene vapour control layer would be a brave choice in a climate where the vapour diffusion may well be from outside to inside for more than half the year. In such climates an internal OSB air barrier/vapour control layer is a good choice. So I would go with Option 1, but with Tyvek housewrap/breathable sheathing membrane applied directly to the outside of the EPS & battens on top.

Note the external membrane shoud be a breathable sheathing membrane, not a Tyvek style vapour barrier as stated. It doesn't need to be reflective, but this may help to keep out the summer heat.

David
- CommentAuthorTimber
- CommentTimeSep 11th 2010
David - Very valid point regarding the the climate conditions (had slipped my mind when writing the above).

Well, on Monday I can rattle though some calcs if anyone would like to give me the highest and lowest external temps likely. However, unless the cabin has air conditioning (cooling) I would suggest that during the summer months, the internal and external temps are likely to be similar (windows wide open), and not sufficiently large to create a reversed interstitial condensation risk. Direct sunlight on the cladding will increase it's surface temp, but the vented void between it and the timber frame should take care of that little issue.

Depending on winter climate, most of the above options will work, but note what david said regarding a breathable membrane on the outside, no a vapour imperiable membrane. Tyvek reflex or housewrap would be fine (again all subject to a condensation risk calc using the correct local climatic data).

Timber
- CommentAuthorstephendv
- CommentTimeSep 11th 2010
Thanks for all the comments! Highest summer temp 38C, coldest winter temp -5C. Don't plan on using an AC in summer, but might have too, all depends on how it performs. Have just gone through a passivhaus design details book and saw a few timber wall designs with taped OSB as the vapour barrier. Their build up was as in option 2 except more mineral wool in the services void instead of EPS. Guess a calc would clear all these questions up
- CommentAuthorstephendv
- CommentTimeSep 11th 2010
Should also mention that winters are reasonably dry, even when night temps drop to -5C, the next day would tend to be sunny.
- CommentAuthormarktime
- CommentTimeSep 12th 2010
Stephen, the Codigo Tecnico de la Edificacion (2009) is your friend.

http://www.codigotecnico.org/cte/export/sites/default/web/galerias/archivos/DB_HE_abril_2009.pdf

For Huesca, at altitudes higher than 600 m asl, minimum average temperature and humidity is 4.7 deg. C 80% RH (January).

For interest, maximum U-values for this zone (E1) are:

Walls 0.74
Floor 0.62
Roof 0.46
Glazing 3.1
- CommentAuthorstephendv
- CommentTimeSep 12th 2010
Thanks marktime! I've been going back and forth with this wall build up and someone pointed me to wood fibreboard products and there use in vapour open walls. They also have a higher thermal mass than EPS and can hold on to moisture... all in all sounds like a nice product to have in the interior of the wall..... so, what do you think of:
- Plasterboard
- 40mm wood fibre board which forms services layer
- Taped OSB as airtight layer and vapour control
- 100mm stud with rockwool
- House wrap
- battons
- cladding

Space is at a premium so would prefer not to have empty service voids on the inside.
- CommentAuthorTimber
- CommentTimeSep 12th 2010
Sounds good to me!! Check cable ratings for use in insulation.

Timber
- CommentAuthorstephendv
- CommentTimeSep 13th 2010
Phew, that's a relief The studs are arriving next week and I was beginning to worry.
- CommentAuthormarktime
- CommentTimeSep 13th 2010
Timber is the expert here so that's encouraging for you. Are you using Pavatherm board?

And I've whispered to you.
- CommentAuthorstephendv
- CommentTimeSep 13th 2010 edited
Will be using the Steico board, since I found a local distributor, who offered it at a good price. Well "good" compared to Gutex at least.

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