Vapour barrier / wall make-up choices

[redtop]

Its a minefield thats for sure!  I could go for the 'traditional' vapur proof membrane, insulation between frame, insulation on outside and then timber clad (has to be timber clad).  But also like the look of woodfibre insulation which tends to naturally draw the moisture out of the frame, and has a larger thermal mass so reduces summer cooking ?  And this is usually used with an internal OSB with a vapour proof coating, which makes for a simpler build.  However trying to get prices for the 'special OSB', and none listed... Which means its got to be pricey.

 

All we are trying to achieve is better than building regs but not passive, we will end up with windows open anyway but i am more worried about making sure the building lasts a long time without damp and also protecting against fire as we are in the middle of a wood and the house is on stilts with a timber ground floor!

 

And all of this against a tight budget.  I just cant seem to work out the ideal approach!  I alsoc ant figure out how you stop the vapour membrane from puncturing when you fasten the battens and how you stop it being damaged in the future when some silly bugger uses a wall screw thats too long (gonna happen at some point).

 

argghhh ?

 

oh, pic of the design below

 

 

05_E_Sections_And_Perspectives-1988101.pdf

[A_L]

FWIW my ideal approach is to use a wall construction that actually does not need a vapour barrier then add one if you want!

 

e.g. from the inside -  ordinary OSB/any insulation you want between studs/more vapour permeable insulation outside studs/breather membrane/well ventilated rainscreen cavity/cladding

 

vapour barriers are really only 'vapour checks', batten nail holes should be partly sealed by the batten itself, you could silicone the back of the batten to increase effect, but if vapour check free construction O.K. anyway..........

 

 

[Russell griffiths]

If you are on a tight budget you can forget the wood fibre insulation, have you priced it up?

are you building the frame yourself or getting a company to supply. 

Your more cost affective method will be a mineral wool inbetween the studs with a mineral wool slab over the studs on the inside inbetween counter battens. 

Why cant you get a price for the vapour shield osb, just a phone call away. 

[redtop]

will probably be an on site stick build, possibly frame if they can sort out site access issues. got a price now for the vapur shield OSB and wasnt as bad as i thought!

[matt-shrops]

How much was the vapour shield OSB and any prices for wood fibre board? I have been looking  and for 50mm woodfibre board it is around 4 times the price of OSB3.

[Patrick]

@redtop

 

 

 The "special osb" is not that special, just look vor vanillin, or passivply plus, i think they are called. Good stuff. Around 17£/board so a bit more than regular osb but saves a step as you need no extra foil vapour barrier. It's much more solid and therefore no problems for accidental rips and piercings.

 

How people avoid accidental holes in their air tight barrier? - service cavity.

 

On a tight budget as well here, we opted for stick build. Frame companies need to make a profit as well and that has to come from somewhere.

external insulation is a great idea, but another working step, plus its expensive. For the same kind of money you can easily double up your stud thickness/insulation.

Leaves the question of thermal bridging.

larsson truss would be 1 way around it.

On 06/04/2019 at 18:27, redtop said:

thermal mass 

Don't use the T... Word on here ?

Edited April 10, 2019 by Patrick