Waterproof membrane - Workshop build.

[garywayne]

Hi all.

Today, I will hopefully finnish the cladding and start putting up the internal boarding.

Sheela, (my wife), has been putting up the insulation and the waterproof membrane. Before I start boarding up I need to tape up all of the joints of the polythene.

QUESTION:-
Do I have to tape the bottom of the polythene to the floor?

If in doubt of what on earth I am trying to ask, please do not hesitate to ask.

 

[Oryxdesign]

This sounds a bit concerning, your waterproof should be breathable or condensation will build up on the inside.

 

[MikeG.]

This sounds a potential problem.....

Could you please give us a complete desciption of the construction of the workshop: wall and floor. Particularly, the wall construction from the outside to the inside.

Whatever you do, do not put any vapour resistant material outside the insulation.

Mike

 

[jasonB]

Poly fixed to inside of the studwork before boarding the internals is correct. It will stop any moisture layden air form condencing within the insulation and making it damp (interstitual condensation), the point at which this can happen without a barrier is called the "dew point"

As for taping the bottom of the sheeting, it depends what your floor construction is, if you have a DPM they yes try to seal it to this.

The breathable membrains should go under the outer cladding to allow any moisture to escape but not let water in.

Jason

 

[garywayne]

Hi guys.

Wall construction, from the OUTSIDE IN.
1/ Featheredge cladding, (treated).

2/ Breathable membrane, (waterproof side facing out).

3/ Insulation within the wall framing.

4/ Polythene sheeting.

5/ Moisture resistant 18mm OSB.

Workshop base, from the ground up.
1/ Sand.

2/ Polythene.

3/ Concrete.

4/ DPM between the base and the wall framework.

I hope this is enough detail.

 

[MikeG.]

Gary,

OK that's fine. Ideally the Vapour Barrier in the walls laps and is taped to the DPM under the floor, but this isn't critical in an outbuilding.

Ideally, but too late I guess, the timber framed wall should be on a brick plinth at least 2 courses high. Furthermore, the breather membrane should have an airgap between it and the back of the feather-edge boards....ie, you should counterbatten over the stud positions. If you do this, don't forget an insect mesh at the bottom (which shouldn't have a horizontal batten).

Sounds like you'll have a great workshop!!! You know, of course, that it will never be big enough!!!

I look forward to seeing the photos.

Mike

 

[Oryxdesign]

Sorry Gary I just re-read your post and you did make that clear. I think you have the answer now.
Simon

 

[CWatters]

There was I was skipping down this thread ticking off the boxes feeling smug that I'd got my design right then wham...Insect mesh! Thanks for the tip.

 

[MikeG.]

Colin,

a good insect mesh is the stainless steel plasterers corner bead (fine mesh type). At 25mm wide it is perfect for batten sizes normally.

Mike

 

[motownmartin]

.the breather membrane should have an airgap between it and the back of the feather-edge boards....ie, you should counterbatten over the stud positions. If you do this, don't forget an insect mesh at the bottom (which shouldn't have a horizontal batten).


Mike

How important is this airgap? what are the consequences if you don't have an airgap?
I ask these questions as I plan to build my own, one day

 

[MikeG.]

I've answered this in your new thread (Workshop Wall)......

......but yes, the airgap is really important. Moisture getting through the cladding (it will happen!) and vapour passing through the wall and condensing, both need air movement to dry them out. Insect mesh top and bottom.....otherwise your workshop will be surrounded by wasps nest.

As you are just at the planning stage, don't forget to build a 2 course high brick plinth below your timber frame.

Cheers

Mike

 

[motownmartin]

.As you are just at the planning stage, don't forget to build a 2 course high brick plinth below your timber frame.

Cheers

Mike

Thanks for the info Mike.

I plan to have a wooden base built on concrete pads