Wall Ventilation

[dtl]

Hello,

Rubble infill field stone walls, with suspended floors and underfloor ventilation.

I am insulating between the joists under the floor with kingspan.
I am insulating the between the wall studs with kingspan.

Is it OK to run floor kingspan up against the stone walls and then put a piece of DPC against wall and then spray foam the gap between the kingspan and wall to stop draughts up the wall?

Or should there be a gap between kinspan and the wall so that the wall also has access to ventilation?

Thanks

 

[middi]

Hi

your set up is not very clear ( or is it me !!).

Can you clarify if you have, or intend to install, a stud wall against the rubble wall and then insulate.

Middi

 

[dtl]

Hello Middi,

Yes installing a stud wall against the rubble wall and then insulating,

thanks

 

[middi]

Ok, now is a bit clearer.

The principle wich you have to work on is that the wall itself will not have to be ventilated because it will not rot, it does not matter if and how much moisture it retains then it can evaporate the same way it got in initially. The main problem you have to overcome is how much of that moisture will be transfered into the inner wall of the building onto the studwork and if you use any dpc will this dpc create condensation on it's outer or inner surface layer where it can accumulate and drip at the base of the wall studs or joists resulting in all sorts of rot problems.
The ideal solution would be to dress any dpc so any droplets of condensation will be channelled away from the woodwork back into the soil or wall. The problem with impermeable dpm's is that they will attract condensation at the slightest ot temperature flactuation and unless an adequate air flow is maintained water droplets will form. you can certainly use a dpm directly against the wall ( the wall will not suffer) and, ideally. the kingspan directly on this and then the stud wall with a cavity. as long as you provide for condensation on the outer surface of the dpm gained from the porous jnner wall to disperse away from the joists ends.
By leaving an air gap between the stud surfaces, any moisture from within the building that has manged to gain access will have plenty of ventilation and time to find it's way out the same way it got in.

I hope this will help you think in reaching a solution to your particular problem.

 

[dtl]

Middi,

Thanks for the information.

Will water move across kingspan or spray foam bridging between a wall and timber?

Thanks

 

[middi]

Water will not permeate through kingspan wich is encased in aluminium foil. As a matter of fact if you tape the joints with aluminium tape ( made for the purpose), no moisture should permeate from the exterior wall into the building therefore avoiding the need of dpm, exept to dress the kingspan at lower part where the stud/beams end.
Some foam sprays are not adept to fire or damp, you have to check into this as to the best type for your situation.

Middi