How to install new floor over enclosed deck?

Question

Hi there

I am enclosing our deck to become a part of our interior home, a second living area. The deck is about 35 square meters. We are going to put in Floor Select waterproof hybrid flooring. I am planning to put 15mm h3 plywood as a subfloor on top of the existing h3 pine deck which has 6mm gaps in the planks. There is about 1metre under the deck, it is well ventilated but does get wet ground and some moisture under the planks during rain as we are on a bit of a slope. I wondered if I should use builders film between the h3 pine deck and the plywood to protect the ply? I also wondered if I should use builders film between the plywood and the hybrid flooring to stop moisture rising into the Hybrid built in foam underlay and also as foam underlay can stick to plywood? Also any other advice? There is mixed advice online in articles and forums with some saying to use film at one or the other stage, others saying at no stage.

Thanks in advance,

Mark

MarkRus · Answer

Hi all,

Thanks for the advice! It is very helpful. I got the idea for plywood with hybrid flooring over it from a builder/carpenter who has a small renovation company who did some work on our /living room renovation. It’s good to Get  advice from knowledgeable people. We  didn’t go through the professional planning/council approval process as our deck already has some walls around it, a ceiling over half of it with a high roof above, and we are just replacing a section of wall and putting in some floor to Ceiling windows and swapping a section of polycarbonate roof for colorbond. Then putting in the new flooring. So, we were under the advice and assumption that as we are  enclosing the deck, and keeping the door separating deck from the house, that approvals were not necessary. It seems I should have a consult with , a drafter or a builder, or surveyor Regarding what we are doing and technically if it needs plans and council approval . I Will also have somebody on site again to have a look at the deck and get some more advice on flooring! Thanks so much. I’m very glad that I asked for some advice before doing anything to the floor! .

Dave-1 · Answer

Good morning @MarkRus

I also have a bunch of bells ringing. For the same reasons that @JacobZ and @Nailbag have shown.

A draftsperson would be a good place to start to see if its feasible. Followed by Builders and council permissions.

I have serious hesitation laying flooring over decking as well.

Something else to consider is if you have a low metal roof for your decking area, once enclose the room will become a hotbox. One place I had an add on that was tiled floor but enclosed (they had done it properly with draftsman plans/builders ect and I saw the price) and even in winter it was icy cold and super hot to the point you avoided it in the daytime.

Dave

Nailbag · Answer

Hi @MarkRus

As with @JacobZ comment, you will require a building permit which will require submitting detailed building plans. Enlisting a draftsperson will establish all the build requirements to turn an outdoor space into an internal one. I suspect that providing the external sub-floor is to spec, the treated pine decking would adviserly be replaced with yellow-tongue. You will also want to note the transition heights from any entry points from the exisiting to new exterior floor. Ideally this needs to be the same or 25mm or less in avoiding being a potential trip hazard. These are just a couple of quick considerations.

Nailbag