Replacing Rotten Floor in External Studio - Solutions Please.

[Jamcoops]

First, hello all. New to this forum but in common with most new members I have a problem!

I have a studio in the garden that was constructed by the previous owners on a pre-existing to them concrete base. The building is 8m x 4m, built well and is water tight. When I moved in, I redecorated (previous owner was an artist), put carpet tiles in one half and heavy-duty garage tiles in the other. This was over the existing lino floor. I use the carpeted side for my ‘office’ for my writing work and music recording/playing. I did note a small soft spot in the floor and planned to investigate when I had time.

The time has now come after 18 months! On moving all the furniture out of the area and removal of the lino, I discovered that the whole floor area was rotten:

I have now removed half the overall floor are down to the concrete:

This has revealed the following:

• A concrete base with unknown construction underneath on the natural clay. It is substantial as on the outside I can see about 400 mm of depth, and it looks like the base have been used to take out the gradient of the sloping garden. The slab is level on the surface.
• The shed has been constructed straight off the concrete with four substantial uprights (look 6” x 6”) straight onto the concrete (rested) with 6” x 2” frame between directly on the concrete. Externally the frame is cladded and internally finished with plywood boarding. I was told that there is insulation, but I haven’t confirmed this. The roof is a large plastic type of structure in good condition with a good fall to rear guttering and a large overhang all round. There is a large set of bifold doors on the front with an integrated door to the side.
• A blue plastic DPM layer laid on top of the concrete. Underneath was soaking wet with water and network of roots across the whole floor probably coming from the two large mature Maple trees about 500 mm from the external side wall and the other at the front corner.
• Previously applied bitumen paint around the edges, looks like an attempt to stop water ingress.
• 1” x 2” wood battens had been screwed into the concrete floor through the DPM layer to provide a base for the 18mm plywood flooring.
• A layer of lino was on top of the plywood followed by my tiles.
• The water seems to be worse in the corner pictured may because of a slight fall on the concrete to this corner rather than an entry point for external water. Water has then entered the battens through the screw holes and from the edges of the DPM.
• The floor battens and plywood are all damaged by rot. The building frame is damaged along the wall and the corner upright is significantly rotted.

Obviously, I need to find out where the water has come from. My guess is a combination of slab sweating and condensation plus maybe some ingress from outside? Then what do I do to fix it. My main worry is whatever I do I am constrained by the structure being built directly on the concrete. Thoughts so far are:

• Use resin to repair the rotted upright base and the worst of the rot in the frame along the outside floor.
• Apply some sort of sealant round the edges.

After that I’m a bit stuck. I could replace the DPM and put a new sub-frame in with more depth and better airflow then refloor with OSB. But then the water will build up again and the trees will come looking for the water again and repeat the cycle albeit more slowly because I won’t puncture the DPM. However, the frame will still get wet and rot.

I suppose I am looking for a best-case solution that balances time against the cost of a total rebuild.

All advice and comments appreciated.


Thanks,


Mark

 

[Notch7]

So you have essentially 2 things needing remedial work: the replacement floor and repair to the side frames.

The starting point really is knowing the detailing of how the frame sits on the concrete, how the cladding finishes to the concrete and whether there is a cavity behind the timber cladding.

if you have a few outside pictures from further back showing the whole structure that would be very informative.


Personally I would say if the concrete floor slab is solid, level and not cracked you could clean it up, lay self level to get it perfect if needed, put down a DPM or paint a liquid one on, put down 50mm celetex, tape all joints then fit chipboard flooring waterproof grade.

the frame can be cut out and repaired where required, but you need to solve the damp ingress so will need to know the existing detailing to suggest a way forward

 

[Jamcoops]

Cheers. Added some more pictures below. From what I can see the frame is just resting (or screwed) directly on the concrete base. There is a cavity between the exteral and internal walls but I am not sure whether it is filled or not.

 

[Deluks]

The punctured DPM is the likely culprit, but the detailing around the edges might not be helping.
Follow the suggestions above.

Also check the fall on the roof and that the guttering is working as it should, make sure the water butt isn't full and overflowing onto the structure.
Might be worth digging out all the way around and putting down shingle, just increase the gap between the ground level and the cladding, so that it looks more like the last picture and less like the middle two pictures.

 

[Jamcoops]

Thanks for the replies. I now have a plan:

• Dig out externally to expose the slab all round and then back fill with shingle where needed.
• Rebuild the rotted upright with resin.
• Use a sealant all-round the inside edge of the building. Can anyone recommend something?
• Apply liquid DPM to a clean and level concrete floor. Can anyone recommend something?
• Install 50mm Celotex straight onto concrete floor taped up.
• Waterproof T&G chipboard on top (floating floor) fixed using expanding PVA wood glue.
• Heavy Duty garage tiles on top for the workshop area and carpet tiles everywhere else.

Two questions:

• Will adding vents through the floor into the studio space help with moisture? Does air flow round the Celotex?
• Will this floor take the weight of my Harley Davidson on a workshop stand?

Many thanks,

Mark

 

[Deluks]

The insulation doesn't need ventilating. Tape all the insulation joints with aluminium tape.

The bike on a stand sounds heavy, you might need to put a couple of sheets of ply underneath to spread the load.

You can also get 38mm t&g chipboard flooring, sold for use in warehouse mezzanine floors, although it costs about twice as much.

 

[Jamcoops]

Thought I would do an update on this.

1: Stopping water getting in. The previous owners had landscape gardeners in. They built up earth above the level of the concreate slab and DPM and chucked their waste down the back doing the same. We dug this out creating a trench all-round the building below the level of the slab. Then we installed a perforated field drain and gravel to take water away. We also re-routed the guttering to take water away downhill from the building. This all went into a soakaway with a further channel taking water away further downhill when it filled. The ground here is clay so no chance of creating a proper soakaway as it just creates a tank! Water ingress solved.

2: Rotted wood. Where the water was getting in and where the tree outside had placed a network of roots the wood was pretty rotted. This included a wooded expansion joint in the floor. All of this was chased out, wood hardener applied, word replaced and then gaps filled with epoxy wood filler.

3: All the electrics are being redone with extra sockets and light switches all at waist level.

4: Floor. This is going in this weekend. DPM first, the 50mm Celotex, then 18mm OSB. Finally, the whole thing will be covered by Duramat floor tiles.

I’ll post some photos when the floor is in.

Mark