Replacing solid woof floor with plywood + engineered in conservatory

[Eric Anderson]

Hi everyone,

Please bear with me as I'm new to all this. I'm planning to lay engineered wood flooring throughout the house, including the conservatory. I have the flooring itself and 3mm underlay with a vapor barrier provided with it for the purpose of laying the floor floating on concrete (rest of the house).

Having taken up the old solid wood flooring in the conservatory, I've discovered that it has been installed directly on top of the joists, nailed down, with some sort of DPM stuck to it. There's insulation between the joists, see picture below.

As the engineered wood is quite thin (13mm), my plan is to glue + screw down a layer of 18mm plywood to the joists, then install the engineered wood floating on top.

1) Does this sound like a reasonable plan?
2) Do I need / should I use a DPM under the plywood? Under the engineered wood?
3) Can/should I use the underlay provided for floating installation on concrete (that includes a vapor barrier) between the plywood and engineered wood?
4) Do I need to treat the plywood, seal it etc before installing?
5) Will the plywood need expansion gaps, and if so, should I leave gaps between each sheet or lay them flush and only leave gaps around the edges?

Many thanks for your assistance,
Eric

 

[crazydaze]

generally sounds ok to me other than you can't use your vapour underlay, you need the non vapour type such as Duralay Duratex.