Tyvek or Not to Tyvek

[SquiddySid]

Long time reader, first time forum poster!

Right then, I've got myself an 1850's cottage (Great) although it turns out now it needs a fair bit of TLC (Not so great). Current project is sealing up the front door (leaving the side door as main entrance) with an insulation sandwich.

I'm planning on putting 5.5mm ply onto the frame as the door profile has horizontal supports, followed by 50mm Celotox within a frame and then another 5.5mm ply to finish. I'll also be sealing the door exterior outside edges with sealant, covering the post box etc...

Question is...do I need a some sort of condensation barrier before the first bit of ply. I'm thinking it should be OK, though someone has put some doubt to my thoughts.

Any clarifications would be great.

 

[cjard]

"Your projects" forum is more for writing blogs than asking questions..

As to the question, general timber frame construction technique is to have a timber wall with infill and overfill insulation, sheathed at least on the outside with OSB or ply.. over the outer layer goes a breathable membrane and over the inner layer goes a vapour tight membrane. If you think your project will essentially be creating a mini timber frame it's a good design pattern to follow.

Tyvek Supro is breathable roofing felt, though Tyvek Housewrap is cheaper per sqm for purposes of sheathing walls, it comes on bigger rolls. You'll probably have more use for a roll of supro felt in the future. Glidevale Zytec Protect is the same thing but cheaper. If you don't think you'll use more than a few metres of the stuff over the entire course of your project then it's senseless buying a fifty quid roll. PayPal me a couple of quid for the postage and I'll send you some