Cellar Conversion Advice Requested

[RaringCoder]

Hi people,

Just signed up to post this topic, but I actually hit the site with fair frequency given all the DIY I do.

I have a cellar that is 69" high from floor to ceiling, with a window to the front of the house. I have up-rooted a paving slab and dug down to find the bottom of my foundations - 17.5" below the floor - sat on dense mud / clay. The wall is (or should be) double brick with a cavity. The last two layers of the foundation brick are stepped out by half a brick, and I presume don't have a cavity.

I'm looking at converting this fully into a cellar that meets regs to be considered habitable.

It has 2 external walls, 2 internal walls (these walls contain the staircase in an old 2-up 2-down terrace), and 1 party wall. I'm sure of the 2 external walls being cavity and 1 of the internal walls being single brick. The other internal wall and party wall I've no idea about.

I want to achieve at least a 2m clearance, meaning I've got to go down another 9-10", this doesn't include space for the floor itself. I've no idea what the floor should be comprised of or what regs it needs to meet. I immediately thought of a floating concrete solution, but have no idea about insulation.

When it rains, the floor also gets rising damp coming through the stone. I have had one small puddle of standing water before on a really bad day, so I presume the tanking is going to need some active drainage.

I'm looking for advice on the flooring, whether foundation pinning is required / what circumstances it is required in, and tanking options for the damp walls (not wet to touch, but definitely damp, I think rising).

Thanks in advance for any/all replies. I'm in Macclesfield in case anyone knows of a local specialist worth contacting.

 

[flameport]

I'm looking at converting this fully into a cellar that meets regs to be considered habitable.

Unless you like throwing large sums of money away, don't bother.
It will be very expensive, time consuming and even then could turn out to be a total mess when finished.

If you want to extend the property, find another way.

 

[RaringCoder]

Hi. I was under the impression that the cost becomes prohibitive if you need to dig out a lot of the cellar, I've only got a thin layer on the floor to dig out.

Unfortunately, there is no other way.

 

[flameport]

Hi. I was under the impression that the cost becomes prohibitive if you need to dig out a lot of the cellar

Quite right, although the cost is likely to be substantial even if no digging out was required.

I've only got a thin layer on the floor to dig out.

Are you sure?

Currently 69 inches floor to ceiling.
A realistic minimum finished height would be 84 inches.
An insulated floor slab with a finished floor on top would be 12 inches or more.
As a minimum, you need to dig out to 96 inches - 27 inches below where you are now. In reality it will be more than this, since you already know the foundations are only 17.5 inches below the existing floor.

 

[RaringCoder]

Thin is relative as there is already 69" worth of mud I don't need to remove. Removing mud is also something that can be done fairly cheaply. The expense comes in to do with the foundations / moisture management.

I've not decided on the ceiling height yet, but your information on the floor depth is useful so thanks.

The only extensions space that will yield a smaller room is the loft - which has it's own complications and is again very expensive.

 

[Static]

If you are still intent on doing the conversion you should do a trial pit to find out how deep the foundations are.. chances are the foundations arent that deep and you will need to underpin to achieve the headroom you need..

You will probably find the loft converstion alot less expensive..

 

[RaringCoder]

Hi, I dug 5 pilot holes in the cellar over the weekend and each wall has different depths and types of foundation.

Loft conversion quotes are frequently in the same region as cellar conversions. If I wanted a dormer window to make some usable space I'd need to start altering the structure of the loft as well, and I'm not sure if dormers include planning permission requirements. And finally the rafters are only 3x2 ish so aren't up to the task of supporting a floor.

With the cellar I've found a specialist who is happy for me to dig as low as is safe, then they will dig out and underpin the foundations and floor it. Just waiting for a quote. The rest will be done by myself and friends/family, so overall costs should be reasonable.

The catch-all "lofts / extensions / moving house is cheaper" doesn't readily apply to my situation yet, though it may do once I've confirmed a quote based on my findings.

 

[RaringCoder]

Just a quick update. (Very) Rough ball-park from a reputable structural engineer and contractor is £5500 for digging out to a little below foundation depth, underpinning, and flooring.

I didn't think that was too bad, but again, that is only a rough guesstimate based on dimensions.

 

[Static]

Remember to add costs for building regs and party wall agreements, as well as tanking..

 

[RaringCoder]

Yeah I'm aware of those parts, not sure how building regulations incur costs on top of the work though, I thought the work would be done to regs anyway.

Tanking is being tackled separately, but getting the thing structurally sound for being a room is task one. I can do other parts of it cheaper for various reasons.