What to lay below LVT (exposed joists)

Zol

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7 May 2025
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United Kingdom
Hi

I have a huge DIY project in the works and am trying to figure out the best way of doing the flooring.

Due to a burst pipe in my 1920s Victorian house, I've got to do a large renovation. Asbestos has been found beneath the old LVT and laminate with the ACM Tiles stuck to the original floorboards with a bitumen adhesive. Everything will come up exposing the joists which are twisted and not level (with some rotten at the ends and loose from the wall).

The plan:

Remove the rotten parts

Sister all the floor joists using C24 timber with M12 bolts, 4mm thick 40mm square washers at either end, with double sided tooth plate timber connectors between the joists.

Joist hangars on the sister joists, where the original rotten joists are to be cut away.

Use a laser level to find the highest joist and sister the joists to that heigh (leveling the floor)

I have some confusion so questions below:

1. Does this sound ok?
2. Any product recommendations for dipping the cut ends?
3. As I need to raise the floor to match the rest of the house for laying LVT throughout, do I need to lay T&G OSB on the joists and then some sort of flooring plywood? Or can I raise the joist height with the sisters and just lay either OSB or flooring plywood and then the LVT?

I have no issue buying the OSB or flooring plywood or both but if raising the joists is an option without a negative impact it might save me a few £££ on not buying either the flooring plywood or the OSB. I think I can use the laser to get the joists pretty level.

This is a first big project for me so all the above is just from research. Any/all advice is much appreciated.

Z
 

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