How worried should I be? Cowboy builder - cement, no DPM, incorrect fixings

[Period_Property_Noob]

Hi folks,

Long-time lurker, first time poster.

So I've got a bit of a pickle - a builder ignored a lot of my requests on a project and I'm trying to gauge how worried I should be. I don't work in the trades but I've done a property reno in the last few years basically just using the internet for research.

I've got a side porch on the side of my 1850's miners cottage, which is over two levels. The house is on a hill, and Ground floor is partial basement, first floor at street level. Construction is sandstone masonry at ground level, transitioning to solid brick.

The porch previously had 5" thick sandstone slabs for a floor, supported by a very rotten roughed out tree trunk that was not visible . Ground floor had a very old concrete floor in very poor condition. Previous owner fitted a bathroom (poorly), which had multiple water leaks that were leaking for an unknown period of time probably in the order of years.

Owing to the longstanding issues we decided to rip the old sandstone floor out and replace it with a joist floor, fitted to the walls with a large timber joist bolted to the walls

Three issues - that I raised with the builder at the time, which are now causing me increasing worry:

1) The builder patched a lot of the damage on walls with what looks like a very strong sand/cement render. There's probably a band running around the perimeter of the room 30cm high where the existing lime plaster has been replaced with a sand cement render to make the walls flat. I offered him a bag of NHL 3.5 that is very well sealed and has been open less than a month but he declined.

2) The builder used ordinary building screws rather than what I've always known as 'joist nails' (twisty galvanised nails). When I challenged him, he placated me with a few extra nails in the empty holes in the joist hangars from his nail guns. Positively, the floor has been very conservatives constructed with respect to joist spacing (small span < 3m, joist spacing < 400m).

3) There's no DPM between the wood and the cement / masonry bedding. I'm particularly worried about damp bridging into the wood and causing it to rot.


How worried should I be?

The original plan for the room below was to insulate the joists with some vapour permeable rockwool type insulation, wrap the whole porch in wood fibre EWI and then use the basement as a plant room.

Thanks in advance, etc.

 

[paulc]

2) The builder used ordinary building screws rather than what I've always known as 'joist nails' (twisty galvanised nails). When I challenged him, he placated me with a few extra nails in the empty holes in the joist hangars from his nail guns. Positively, the floor has been very conservatives constructed with respect to joist spacing (small span < 3m, joist spacing < 400m).

3) There's no DPM between the wood and the cement / masonry bedding. I'm particularly worried about damp bridging into the wood and causing it to rot.

The joist hangers means any fixing will be under shear loading. It shouldn't make much difference if they are screws or nails as long as a) they are long enough, b) big enough cross section.

A lack of DPM would be of concern to me also. If you have taken up more than 25% of the floor in one room, Building Control should have been notified. They may well take a dim view of no DPM.
Assuming the floorboards have yet to be fitted, it might be possible to jack the joists up and slide some DPM material under them.

 

[Period_Property_Noob]

Thanks. I took a similar view.

Sadly there's a few massive sheets of well-nailed down plywood on the floor. And owing to the cement packing the wall out, there's no space to shim anything. My other worry is the because the builder used a mixture of bolts and resin fixings applied when the joists were already on the wall , any seepage from the resin fixing will mean the joists directly attached to the wall will be very, very well stuck.

The only mitigation is that by chance I bought pressure treated class 3 joists ('external use but not in contact with ground'), because I knew it was going to take me a while to get around to fitting out the space below. Although I have no idea how much that might swing a bilding inspector.

 

[aockenden]

I probably wouldn’t worry about the first two items. Small amounts of cement (while certainly not ideal) shouldn’t make a huge difference to the overall building function.

The lack of a DPM between joist ends and the masonry is pretty shocking tbh, especially because this is ground floor where moisture will be coming up from below at a higher rate. Treated wood possibly helps that issue but it’s still a mistake.

In this new suspended floor ventilated underneath? Sounds like there’s a basement beneath or did I get that wrong? In any event, is the space beneath ventilated?

 

[Period_Property_Noob]

Thanks Aockenden.

So the new floor is above a storage room that's recessed into the ground on two sides.

That probably isn't a very good way of explaining it - but the garden level in my property is a storey lower than street level.

So the new floor currently has about 10 ft of airspace between it and the ground. Though this will reduce to approx 7ft once we've finished replacing the floor below with concrete. Currently it's excavated but we're waiting a few weeks to put hardcore etc. down. One thing to say though - it isn't that he's failed to use a DPM on the 'joist ends' - it's actually the bearer timber (a bit of 6x2) that's mechanically fixed to the wall that lacks a DPM.

The plan is eventually we're going to install 2x air vents into perpendicular walls. Currently the space is fairly well vented owing to the door being an old-school 'shed style' door.

Though I don't know how much air flow will actually reach the timbers - we had drawings done some months ago and the plan was to lag the joists with rockwool-style breathable insulation.

 

[a twig]

Just to clarify things in my head, there is a bearer timber perpendicular to the joists that is resting on the floor without a DPM between in and the floor?

Or is that bearer timber on piers / dwarf walls?

 

[Period_Property_Noob]

Hello there,

Apologies for the delay - my better half is 39 weeks pregnant and I have had other priorities. Though apologies if this qualifies as 'resurrecting' a dead thread.

I thought folks might appreciate an update.

With respect to the property and "a twig"'s comment: a bit of both.

On 3 sides it's a timber bearer directly bolted into a *wall* (6' above the ground), with no DPM between timber and wall, and no DPM in wall generally.

On the 4th wall, it's also a timber bearer bolted into the wall, but there's also a bit of a pier / ledge directly under the bearer.

I was able to catch up with the architectural technician who did the drawings. His assessment was that with a few mitigations it was unlikely to rot in my life time.

What I'm doing is:

1) Doubling up the pressure-treatment with an ordinary, off-the-shelf, wax free wood preservative, to improve the resistance of wood to rot.

2) Switching the location of the insulation from *between* the joists, to directly under-neath the joists, secured with netting, to (a) improve airflow around the joists, and (b) make it easier to inspect the bearer periodically.

3) Slightly modify the design of the floor below. The plan was to originally put some rigid foam insulation (celotex/kingspan) between the hardcore and concrete. Instead, in case the floor ever needs propping up to facilitate repair work, we're removing the insualtion, but switching the hardcore to a 'foamed glass' product that appears to act as both an insulation, but is also load bearing.

The view of the architectural technician is that between the air flow, the fact I'm fitting a breathable EWI to the walls, alongside the other mitigations, should mean that there's minimal risk of damp transferring into the wood and with periodic maintenance every few years to inspect the wood, we should be fine.

Thus far, apart from the hassle, the only permanent disbenefit appears to be that shifting the insualtion below the timber is probably going to make the electrical underfloor heating I had specc'd considerably less efficient. But I think I can live with that given other priorities presently.

Thanks all.