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Strange Subfloor and Treating Woodworm Infestation

Postby David_R_Jones » Thu Aug 15, 2019 11:31 am

We could really use some advice and some rough ballpark estimates of what it might cost to fix or remedy these problems so any help and guidance would be really appreciated

We're buying a house (built in 1938, Shrewsbury) which has an active woodworm infestation. We were planning to spray the floorboards that currently exist with pesticide. However, when we pulled the boards up on the ground floor, the subfloor was unusual. There are 3 rooms that need treating, the hallway, living room and dining room. Under the Livingroom and Dining room, it looks like concrete has been set in-between the joists with about an inch gap between the concrete and the top of the joists that suspend the floorboards. When we pulled up the board in the Hallway, it was almost resting on a substance that we believe might be ash or shale (it was mostly grey-black, I've included a picture of some pieces we took from underneath the board). We had originally intended to keep the floorboards, but since they are tongue and groove and we cannot spray under the subfloor there will be considerable damage done to the floorboards if we plan to pull up every board in order to treat them with insecticide.

substance under hallway floorboards

Here are some questions we'd like some advice on;

    Are these kinds of subfloors an issue?
    What would be the cost to put Chipboard down in the Living room & Reception Hallway? We're planning to add an extension at some point and we will refloor the dining room at that point.
    Should we rip out the concrete? Will the joists need replacing if we do? How much would this roughly cost?
    We're speculating that the ash/Shale substance in the hallway should definitely be removed as it could be concrete that has sulphur damage if this is the case, does this mean we should we rip up the concrete in the other rooms too?
    Will the joists be safe from woodworm attack if they are embedded in the concrete as they are?

I've included some rough room measurements for an idea of the scale of the work that would be needed.

Reception hallway: 16'4 x 9'1 (5.2m x 2.8m) (has staircase along one side)

Bay fronted lounge: 14'11 x 11'11 (4.55m x 3.63m)

Dining room:14'0 x 10'10 (4.27m x 3.30m)

Any help at would be appreciated, we're trying to work out the costs before we renegotiate our offer with the vendors. I'm aware that this is a can of worms that we're opening, we don't need full detailed quotes but just indication of how much this might spiral into in a worst-case scenario.
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