Kitchen renovation: is suspended timber sturdy enough for tiles + mould on walls/cabinets

[TofuSpaceship]

Hello all,

we are re-doing the kitchen, it is in an extension off a terraced Victorian house.
The kitchen size will be roughly 2.38m x 6m.

I have a couple of challenges coming up, questions underlined.

A. the floors of the main building are higher by 18cm than the current kitchen floor (which is only concrete+vinyl on top, as we speak). The idea is to build up the kitchen floor to the same level as the dining area, and in the process we can wack some insulation in.
The final finish is going to be tiles.
I can probably get away with joists of 47 x 122 seeing as the max span is 2.38m, however that leaves me with 58mm left to the dining room level. In those 58 mm I need to fit ply, I was thinking 18mm for extra sturdiness seeing as the final finish is tiles; then tiles and screed (extra 10mm?); insulation will be insert in between joists, I am therefore left with 30mm clearance all going well.
- Is there any (thin) insulation that I can lay on top of the joists to guarantee extra warmth, as right now the floor is really very cold?
- Do you think that 30mm is enough clearance to guarantee sub-floor ventilation AND will the timbers and ply be sturdy enough for a tiled floor kitchen?
To be noted, the span is north-south, south wall is facing the garden of the neighbour, so no air bricks there. We will have air bricks on the north side.

B. The kitchen has always suffered from damp problems. Cabinets and wall units, especially in the corners, have always had damp issues and a musty smell, even the cabinets on the south corner adjoining the neighbour garden, so the back wall of that corner should see some sun, at least in spring/summer.
We have lived in the house for 2.5 years, last year the parapet located one floor above the south kitchen wall has been redone due to renovation upstairs. We are aware approx. 10 years ago the kitchen had been injected at 1m high for rising damp (as if it helps).
I can see now that the kitchen has been ripped out, there is light mould on the plaster in the bottom corners, screws fixing the skirtings are rusty, a backbox (1.5m height) in the south wall is rusty too.
It could be either that the water was percolating from the old, crappy parapet wall, or it could be "rising damp".
- Either way, what's the best we can do at the moment to make sure that our new kitchen cabinets will not go musty in a couple years?
To be noted, we leave window open and fan on when cooking, boiling kettle, etc.

Going now back to point A, due to the above, i.e. not knowing how up to scratch the kitchen extension is and if it has a DPM / DPC at all, you understand that I would want for the joists to be suspended wall to wall, rather than laying them on a concrete floor which could be without any DPM. I would use galvanised steel joists hanger to make sure joists don't rot over time.

 

[bobasd]

why dont you post photos of the kitchen's inside walls and floor, and outside walls at ground level?

 

[TofuSpaceship]

sorry, hadn't seen you reply. Here are some pictures

 

[bobasd]

can you post pics showing both sides of the parapet?
and a pic showing the 180mm floor difference threshold?
are the walls of the extension cavity or solid?
how is the main house suspended floor ventilated?
does the kitchen have air bricks or an extractor?

any DPC in the wall(s) has been bridged over.
so far there's no sign of a DPM.

your interior plaster should not be in contact with the solid floor.
the external render, behind the soil pipe and below the dashed render, should not be in contact with the ground.
its probably best to hack off to 300mm above any damp or condensation signs - go back to brick.
and then render back up in 3:1 sand and lime render with, say a Limelite skim finish.

if you raise the floor by 180mm then the base units might be higher than the window sill, and you might meet further difficulties?

 

[TofuSpaceship]

sorry for the radio silence. Have been quite busy with plumbers, builders, SEs and the lot.

I cannot post pictures of the parapet, our study room is above the kitchen and the parapet is above the study room. When the parapet was done last year it looked all nice and sealed and well made.
The walls of the extension are cavity, or at least so I assume based on the walls that are upstairs in the study room.
The main house is suspended floor, not so well ventilated (I have another post somewhere with an ongoing discussion with you about water in the living room floor; that is a mud pit at the moment and I am not dealing with it)
Kitchen has no air bricks currently as it is a slab of one inch concrete over the ground and there is a little extractor fan which we always turn it on when cooking, kettling, etc.
The builder has dug out a trial pit where the steel pillars are bound to go in and I can see there is indeed a DPM between ground and concrete slab.

Externally, shouldn't there be then any render at all between ground and dashed render? Of course it doesn't make it right, but isn't it the norm, I think I seldom see (looking bottom up): ground, blocks, render? Usually render is covering the blocks, as they're dead ugly!

Thanks about the remark about base units and raising floors. We will anyway put a different sized window in.

On the topic again, we've had chat about it with the SE too and we came to the following conclusion.

Instead of doing a suspended timber floor to meet the 180mm gap to the dining room floor, we are going to build a floating floor.
In essence, another DPM on top of the current concrete slab, thick insulation (probably 130mm), two sheets of ply, screed and tiles.
Further, to address the issues of musty cupboards and preventing it from happening again with the new cupboard, we are going to wrap every wall with 27mm Gyproc ThermaLine Plus.
In essence the whole room is going to be wrapped so hopefully there won't be any cold spot where condensation will form. Plus with the new patio doors and a proper extractor hood we can make sure that there is never too much moisture buildup in the room.

QUESTIONS:
About the floor
1. Would you bother using a self levelling compound onto the current concrete slab, before putting the insulation? Checked with a 6 feet level it is quite level across every direction, not exactly spot on but always within the two reference lines of the level.
2. Can I have your opinion whether it would be OK to run new water main 25mm or 32mm PVC pipe AND main gas pipe (also 25mm or 32mm) above the concrete, by means of cutting a notch in the insulation slab? Should add I will be cutting two notches, as the water main will run at the opposite side of the gas main.
3. This is a very personal view of course: with 130mm insulation underneath and a tiled floor, can I expect for the tiles not to be dead cold, or will they be regardless? I am still tinkering with the idea of having supplementary UFH to take the edge off the coldness of the floor.

About the walls
4. Would you put a VCL between the current wall plaster and the 27mm thermal plasterboard?
5. If VCL is a yes, would you put cables between blockwork and VCL or between VCL and plasterboard? Probably it doesn't matter much, as unfortunately we are already going to break the VCL where we will be installing sockets (we want them flush to the wall)
6. I am aware that I should down-rate cables if they are embedded in insulation; however in this situation where there is insulation on one side only (and the other side is an external wall, thus cold) and it is a mere 18mm of foamy stuff, is it really needed? Not really worried about the kitchen ring, as it is indeed a ring the load will be spread. More worried about the cooker and boiler (two separate) spurs.