Converting a cellar to a workshop - practical considerations

[StevieB]

My current workshop is in a cellar - bare brick walls, uneven surface etc etc. Typical Victorian cellar. What I am planning to do is line the walls to make it a proper room, but it needs doing to a budget. Dot and dab is no good as the surfaces are far too uneven and there are a number of pillars etc in the way. I am therefore really only left with timber or metal stud walling. Metal seems to be out due to cost - £6 per stud as opposed to timber which is a third of that price :shock: looking into this more closely I am left with a number of questions:

The cellar is small enough as it is so I want to minimise decreasing it further. What is the minimum stud sizes you would consider? 50 x 100mm (2" x 4") is overkill as ther is no roof to support and brick walls all round. I am torn between CLS at 63 x 38mm or I could go down to 25 x 38mm. There will be a brick wall all round but the walls are uneven enough that to get the studs vertical it may not be feasible to screw to the wall. I will have a sole and head plate fixed securely but will 25 x 38 be strong enough for a stud wall? There is no roof to support, only wall cabinets which I would french cleat into the studs.

Second question is insulation. Standard glass wool loft insulation is cheapest and really my only option as this has to be done to a tight budget. Do you lose insulation if you compress this stuff ie fit 100mm insulation into a 63mm or even 38mm gap? Or given the price is not much greater for 170mm insulation should I squeeze that into a 63mm gap? There will be variable distance between the stud and the wall itself but not a great deal extra on top of the stud depth.

Third question is plasterboard - 9.5mm or 12.5mm. Apart from strength due to increased thickness, is there much thermal efficiency in having thicker plasterboard? OSB or ply is not suitable as this is a cellar and it needs to look like a decent room, not a wooden workshop (so I have been told!)

Fourth question - damp proof membrane. Looking at cellar tanking websites, a waterproof membrane (plastic sheet) sits between brick wall and back of the stud so any water through the bricks drops down into channels and a sump. My cellar is dry and has been for the last 3 years since we moved in so I doubt it will flood. Thus do I need a membrane is the question? I dont want to induce sweating between the brick wall and the membrance, but similarly do not want damp penetrating the stud wall. Like all cellars its musty and rusts tools left lying about so there is moisture in the air - if I convert the cellar to a proper room I do not want to increase this problem due to restricted air flow etc. There are no drainage channels or sump pump at the moment as there is no need and I will not be putting one in.

Final question - flooring. More specifically, it has a sloped one. Across 4m it drops by approximately 3-5cm. Its a concrete floor which is reasonably flat ie the gradient is constant. I can either level it somehow, or live with it. If I live with it will I regret it? How plumb do people get their own floors? I plan to put down chipboard flooring so may have to joist out for that to secure the boards down flat - would you trim every joist to bring the floor to horizontal? Head height is not an immediate concern as I have 2.3M, but I do not want to lose too much due to a couple of pipes which drop below this level.

From a rough calculation I can stud in CLS, 12.5mm plasterboard and 100mm glass wool insulation in walls and ceiling, for around £500, which is really my budget. Would anyone recommend anything different without increasing my budget significantly? I will be posting detailed pics of the process next year when I start (got to do the bathroom upstairs first over xmas, then I can start on the cellar in the spring) but the planning and the anticipation is half the fun of these projects so I am starting to dream and cost things now :wink:

Cheers for any advice,

Steve.

 

[MikeG.]

Looks like my sort of question!

I'll have a go at this at lunchtime........

Mike

 

[wizer]

How frustrating that the basement thing didn't remain a tradition in this country. Basements would surely solve a lot of the problems people have with space in this country. If I was ever to build my own house I'd have a basement, no matter what the cost (or rather I wouldnt build it if I couldnt afford to do that).

 

[agbagb]

I'm looking forward to what Mike has to say on this one.
My experience consists of having had two workshops in cellars. Damp and fusty is the natural state of my cellars. Trying to force anything else can be difficult and expensive. The easiest way to make it workable is loads of ventilation to dry out the walls and floor as it seeps through, cladding the walls will just hide the damp for a bit. The pressure of water in the earth around the cellar will force its way in and around normal membranes. I think proper tanking is fully sealed and allows water to drain away behind it. If the water doesn't drain it will build up.

If Mike has a low cost solution, I'll give it go.

Andy

 

[MikeG.]

Right, Steve...........here we go.....

Firstly, damp:

you say your cellar is dry, yet also say that the air is damp enough to rust your tools. Cellars, even perfectly tanked ones, have notoriously low levels of ventilation and are generally cool........and this is a perfect set of conditions for condensation, particularly if there is intermittent heating used and occasional bouts of energetic occupation!

Ventilation is your answer, and is key to the successful use of this room. I won't go into full tanking systems here (I have never had much faith in internal tanking anyway).

You need to get access to external air. Whether this is up through the house and then out through the wall, or out the the cellar walls and up through the ground doesn't really matter. My suggestion would be to have a pair of 110mm dia. plastic stack pipes, one at either end of the cellar, running up outside the walls of the house if necessary, and capped with something to prevent water ingress (but which still allows air movement). One of these could terminate at high level, and one down near the floor in the cellar, and they should each have an extractor fan attached.........but crucially........one fan extracts from the cellar, and the other extracts from the outside into the cellar (ie, is mounted backwards). They should be wired to come on together controlled by a humidistat. I suggest that small bathrooms ones should be fine, but your electrician will have to size them for you.

That should give you serious air-flow through the place, and remove the musty damp smell.

Before we discuss the walls, there is the question of the floor. If you are happy with it out of level, can you leave it just as it is?

What I certianly woudn't be doing is laying joists and a timber floor. That would create a void where water, if it ever got in, would sit undetected. That is a nightmare scenario.

The alternative is screed, IMO, and then we have to ask if tanking between the existing and the new is worthwhile. This isn't easy......

If you tank it will be protected and therefore effective....but, it will just force moisture sideways for it to rise up the walls. If it did this, I don't believe that there is any effective internal tanking system to be 100% sure of for years. I would always want to tank externally. As this won't be possible, logic suggests that you might be better off not tanking the floor. I suggest that you get some specialists in to have a look (but don't forget, they are salesmen!)

If you do go for screed, you can of course get some insulation in below it.

Right, so you have either left the floor as it is, or screeded it with 70-75mm sand/cement (which, by the way, will produce an enormous amount of water-vapour to dry out over the first few weeks).......now, the walls.

Because we can't trust that the walls will be dry, I think we must leave a ventilated void behind any insulation.........albeit, this doesn't have to be much more than a few millimetres. Furthermore, if there is actual liquid water at the surface of the walls ever, it will need to run down and out onto the floor. This suggests to me that any studwork should have its plate raised off the floor.

What I suggest is to get hold of some quarry tiles, or some stone off-cuts, or even some chunky bits of slate, and space these about every 300 or 400mm. Your plate will then sit on top of this, thus raised some 10mm off the floor.I would use 50x50 treated timber fo the studs & plates, and make a tight frame of this all around the cellar walls, spaced some 10mm off the walls. This feels very springy, and would not work very well without the follow cunning plan.........

Get hold of some spray foam (best with a gun). Spray in dabs of this between the studs and the walls, say every foot vertically. This will really lock the timbers tightly. Between your studs, I would then use Kingspan or Celotex, and the best way to do this is to cut it undersize by about 10mm all round, wedge it temporarily, and spray foam all around in the gaps. When this has gone off, pull the wedges out and spray some more foam in.

The voids are now ventilated at the bottom, but not at the top. We'll come to that.

I presume your cellar ceiling is insulated? If not, I reckon it should be, because you aren't going to maintain it at the same temperature as the house, and also, you will want some sound deadening between your workshop and the house..........(its amazing how disturbing the kids music can be!!!).

Finally, cladding the stud walls. If you want something posher than OSB or ply, I would suggest using MR MDF with the "T&G grooves" moulding. I really don't think plasterboard is a robust enough product for a workshop. The MDF (and you know how I hate the stuff and wouldn't recommend it unless it was just the right product) looks very good painted, and would be perfectly acceptable if the room was used domestically at a later date.

In the middle of each "panel", between each pair of studs, right at the top just below ceiling height, I would cut a round hole and remove the MDF and the insulation, and fit those round soffit ventilators (they are probably 40 or 50mm in dia.). That completes the ventilation of the void.

Presumably, you will be installing permanent heating. I reckon this might be set at a fairly low level, but to run fairly continuously.....controlled by a room stat.

My only remnant worry is the 10mm gap below the wall. We really need an insect proof grill-strip, which doen't impede airflow much and would allow water to dribble out. I can't think of one off-hand........

Hope this helps. Don't forget, anyone else who reads this, that this advice is only aimed at a very special set of circumstances..........a nearly dry cellar. The advice may well be useless for an other circumstance.

Right................where did my lunchtime go?

Mike

 

[RogerS]

Oooh...at last...something I can comment on reasonably authoritatively having battened and drylined out a complete house.

Don't worry about the uneven wall. Knock up a frame that roughly fits the size of the wall. Base plate and top plate then verticals at intervals to match your plasterboard width. Make it square and make sure the base plate and top plate are parallell - that way you can cut all the verticals to the same length. I custom made the first frames in the cottage and what a pain that turned out to be.

Add some cross-bracing (aka noggins). Offer it up to the wall and get it vertical. Then pack out behind with wood offcuts. I used the 63x38mm CLS as it was cheap from B&Q. If you use it 38mm at right angles to the wall then that will give you room to fit in some insulation sheeting such as kingspan - go for Seconds - Kingspan has recently laid off people so I reckon you should get some bargains. If you lay it 63mm out then it gives you more wiggle room to fix your plasterboard.

Personally I'd stump up the money and put a sheet of ply on top and then 9.5mm plasterboard. The ply gives you something to screw your shelves to etc. If you don't go that route then measure where the studs are and take photo's.

Hire a nailgun.

 

[StevieB]

Roger / Mike, thanks you enormously, very sorry to take your lunch hour Mike!

Ventilation is the main take home message I get from your comments. The cellar originally had simple open iron work grilles at outside ground level (ceiling level in the cellar) which allowed ventilation but also rain, snow, insects, rodents, leaves and anything my 3 year old son could poke between the bars into the cellar. Clearly not good for CI tools. Having got rid of the rodents and swept up the leaves, I put perspex over the grilles and sealed with mastic - upside was no rain ingress, downside lower ventilation. I combatted this by leaving a window open in the cellar (allowed air flow but not rain via a light well) although in winter this makes it too cold to work so its only open partially and not continuously for 4 months of the year. No mould in the cellar, but definately musty. An extractor fan in this wndow is an option I hadn't considered until reading your comments, but presume this would work as well as the 110mm soil pipe you suggested?

Dampness and condensation. The cellar is actually two rooms, or one large cellar with a brick partition wall. The front half, approx 12 ft square is concrete floored and the half I have my workshop in. The back half is still cobbles laid directly onto clay. This is where I presumed most of the damp mustiness was coming from, and since its a big job to lift and relay this, and as you suggest there will be alot of vapour to disperes with wet concrete, I wanted to do the cellar in two stages and protect my tools in the front as far as possible before laying a concrete floor in the back.

One entire wall is the party wall between us and next door (no problems there, they have already converted their cellar) so no damp issue on that one, a second is the partition wall between my two cellar rooms, so only two of the four walls are external. These are never damp to the touch or suffer from condensation even after covering the grilles with perspex. To go from this to water pooling on the floor and rotting flooring joists is a big step (I hope!) but if it has happened to anyone else I would love to know now. Not denigrating your ideas at all, just that on a budget I need to be reassured it is worth the extra expense. The mildly sloping floor I can cope with - screeding is time consuming, labour intensive and probably unessecary.

Great tip on the spray foam, hadn't even given that a thought, but dot and dabbing with that on the studs is a brilliant solution.

Kingspan is probably beyond my budget unfortunately, even for seconds. A roll of glasswool loft insulation will cover up to 13 sq meters for 15 quid (BOGOF at B&Q) they did jabalite for £23 for an 8x4 sheet and Kingspan is more expensive than jabalite.

Take on board your comments about MDF v plasterboard. Will think about backing with ply as you suggest then 9.5mm plasterboard over that. Have hung kitchen cabinets on stud walls before by screwing into the studs without any problems but will give this some serious thought.

For a £500 budget, if I can get a sound job that lasts 5-10 years I will be very happy with that. It doesnt have to last forever, I just hate seeing my tools deteriorate due to a poor workshop environment. In the future, when money is not so tight I can do it all again to a higher spec. Will probably want to change the layout by then anyway! So long as the cellar is as good as an insulated timber workshop thats problably all I can hope for on my limited budget. To fully tank a cellar properly will cost several thousand even if I do most of the work. Heck a good timber workshop can cost several thousand!

Thanks again for your comments, much appreciated.

Steve.

 

[RogerS]

Mike...my experience with foam when used vertically is that it tends to drop and fall down long before it goes off.

SteveiB - one more thought. Why not dab to fill out the walls a bit where needed. Then when dry, dot and dab as per normal - dabbing on top of your first dabs. But that will only work with plasterboard and limited structural strength for supporting cupboards.

 

[Jake]

My workshop is in a cellar, but only about 1/2-2/3 of its height is below ground. No insulation except in the ceiling (but doesn't really need it, it never gets that cold because of the ground contact, I guess) and plenty of ventilation from two big (30cm2) air vents and a few ordinary airbricks.

I have a few damp patches here and there, but it is mostly fine. The walls I've left bare brick (or rather original lime wash). I just whack up some ply to attach shelves and stuff to - spacing it off the wall with off cut bits of treated timber so as to keep the ventilation up. My tools don't rust, (despite the SWMBIWSTTBMA insisting on running the tumble drier non-stop at the other end of the cellar).

 

[MikeG.]

Mike...my experience with foam when used vertically is that it tends to drop and fall down long before it goes off.

No problem with a 10 mm gap..........I've done this many times myself. It works a treat. I agree that if the gap is too large there would be a problem.

Mike

 

[RogerS]

Mike...my experience with foam when used vertically is that it tends to drop and fall down long before it goes off.

No problem with a 10 mm gap..........I've done this many times myself. It works a treat. I agree that if the gap is too large there would be a problem.

Mike

Must be related to the manufacturer then as 10mm definitely slides down for me.

Edit: Do you mean 1cm? I agree...thought you meant 10cm.

 

[Jake]

cm don't exist for architects, Roger.

 

[ike]

Through-flow ventilation, while it may keep humidity down, makes keeping the space warm, more difficult especially in winter. A possible solution may I suggest, would be to install a split room air conditioner. Multi-mode functions allow dehumidification as well as heating. Efficiency ranges from a COP of around 3.0 to 4.2 (for each kWh of input, you can get up to 4.2 kWh of heat output). OK, so it's still using expensive electricity, but given that 2/3 of the heat is extracted from outside, the overall running costs would be much closer to that of gas-fired heating.

Another option would be to extend your central heating circuit if possible, and to use a portable dehumidifier, although to have continuous drainage would need a bit of thought, unless there is a already a drain point in the cellar.

Cheapest units start around £300, and can be DIY-fitted. They come typically with 3 to 5m of interconnect, so it shouldn't be too difficult to route from the cellar up outside. The high efficiency models employ inverter technology to drive a DC-powered variable-speed compressor, but are rather more expensive. I'm planning to install a 9000BTU unit in my workshop next year. The model I am looking at also has an electrostatic filter, therefore would save me the cost of a separate workshop filter unit such as a Jet 500.

However, it is still a very good idea to have powered cross-flow ventilation for fresh air and fume extraction.
cheers,

Ike

 

[StevieB]

Thanks Ike. I had been told that dehumidifiers in a cellar were not a good idea since although they dry the air in the cellar they also pull moisture through the walls from the earth outside - not sure whether this effect would be significant in a stud wall lined workshop inside the brick walls (a box in a box effectively) but I could certainly try it once I had stud walls up and lined.

Still not sure whether you lose efficiency from compressing standard loft insulation or not though - anyone know?

Steve.

 

[ike]

Yes, std loft insulation derives it's U value from the air trapped within it, (in fact predominantly so with any type of building insulation product) so compressing it reduces it effectiveness greatly. You would be better off to use the rigid insulaltion board as used in wall cavities. 50mm would give you greater insualtion value than 100 or even 150mm fibre

 

[ike]

I had been told that dehumidifiers in a cellar were not a good idea since although they dry the air in the cellar they also pull moisture through the walls from the earth outside -

Yes, that's true unless you have a vapour barrier behind the drywall. Even without a barrier, there would howver be moisture gradient from within the wall to the surface. As long as a dehumidifier can maintain this gradient, i.e. keep the surface reasonably dry, I don't see a problem - you are still better off as long as you can keep the air humidity down.

 

[Jake]

Cellars have very stable temperatures by their nature, and can cope with a lot of ventilation without getting too cold for a workshop. I'll check what temp mine is at the weekend. It's slightly distorted by the boiler and a bit of CH piping I haven't got around to insulating yet, but even in this cold snap I'm sure it wjll be well above above 10C. You might not want to sit down for a few hours, but I've never noticed feeling at all cold down there.

 

[MikeG.]

50mm would give you greater insualtion value than 100 or even 150mm fibre

Right first time, wrong second.........

A rough rule of thumb is that the solid insulants are twice as effective as mineral wool.

 

[Jake]

Save the money and spend it on tools!

Dry-lining is a poor and complex way of achieving an over-the-top outcome which is unnecessary for a workshop, and creates as many problems as it solves in a cellar, solving those problems costs money, etc.

Up the ventilation, and buy another layer of clothing if you need to.

 

[StevieB]

Why do you say its an over the top solution Jake? I have a musty cold cellar with walls that are so uneven I cannot hang cabinets from without substantial battening. Its noisy to the upstairs rooms of the house and cold from the cellar through the floor to the house is an issue that needs resolving. Dry lining is far cheaper than full tanking and provides a cheap, useable room which looks better than uneven poorly mortared Victorian brick walls and will add value to the house. It also allows the room to be painted white to increase light and eliminated draughts and ingress of wee beasties (insects/spiders etc) from cracks and crevices in the walls / ceiling. If it prevents my tools rusting then it would seem to be money well spent IMHO. For a small initial outlay I solve a large number of problems - if not forever then at least for a few years, which for £500 is an acceptable compromise.

There are alternative and more expensive ways of doing it, finding the balance between what you need, what you want and budget is what we all have to do. At the bottom is do nothing and wear an extra checked shirt and grow a beard :norm: , at the top is full tanking with central heating. I personally think more tools, opening a window and an extra shirt is not the best solution for me.

Steve.