Garage/Workshop construction

[Roger Mills (aka Set Square)]

As you will know from my earlier thread "Size of a double garage", I am - planners permitting - hoping to have a detached double garage built at the front of my property.

I have established that, provided it has a floor area not exceeding 30 M^2, and is made of non-combustible material, it will be exempt from building regs. This is fine from a fees point of view, but also means that it won't have a BCO making sure that it's built properly!

I would like to be able to use it from time to time as a workshop, without requiring too much heat input - which means that it requires a reasonable degree of insulation. I would appreciate your views on this.

WALLS Should they be of cavity construction, filled with insulation - or single brick with some exotic material or other fixed to the inside? What is the effect of the choice on the ability to fix things to (e.g. shelves) or hang things (e.g. ladders) on the walls?

DOOR I rather fancy an automated roller door - like the ones made by Henderson et al - with double skin aluminium which is foam filled. Does anyone have any experience of these? Are they robust and reliable? What are their thermal properties?

FLOOR It will have a concrete floor. It would be nice to have some form of insulation (rigid foam or whatever) under the concrete - but is this practical, bearing in mind that it needs to take the weight of two cars?

ROOF I'm currently undecided about a flat (felted) or pitched (tiled) roof. What's the best way of insulating it? I'd rather like exposed beams from which I can hang things - and to make use of the available storage space if I go for a pitched roof - but still need to get some insulation in somewhere. Any thoughts?

ELECTRICS Haven't really thought about them yet, but I shall need some light and power. I assume that they will have to be Part P compliant, even if the structure is exempt from building regs?

[John Cartmell]

Light & draught.

As a workshop you might want to have natural light wherever possible - but not suffer the draughts from an open car-sized door.

[John Rumm]

Well if you went for cavity, then the inner leaf would typically be some sort of insulating block - ok ish for fixing to but not ideal. If you went for single skin with a studwork frame stuffed with PIR foam then you could clad it all in ply which gives you an easy way to fix anything anywhere. Probably work out more pricey than blockwork though.

I would expect if you laid out a grid of rebar and wired it together before pouring the screed it would be plenty strong enough. It is not really carrying the load of the cars - it just needs to spread it a little before it is transferred to the jablite (or whatever you use). A quarter of a tonne (each wheel) over say 1m^2 ought not make a noticeable impact on the insulation.

Flat roof with exposed beams would suggest a warm deck construction - quick and easy. Nothing to stop you from pitching it a little either to get better run-off (or use steepish firrings). Tiles and a pitched roof would probably look nicer though - again you can do a warm deck type of construction with those IIRC. Have a poke around either the kingspan or celotex site I have a feeling they had an application note showing a way of doing this.

You could argue that if building control are not involved you can do whatever you like ;-)

Some questions that need thinking about first though: Is the building to be joined to the house or some distance from it? How were you planing on heating it? What sort of workshop tools do you expect to want to use out there?

Having come out with a power budget, add enough contingency to it to make sure you cover any likely future use. If you are going to the hassle of digging a trench for a SWA you may as well make it a big one since the cable costs will be negligible in the grand scheme of things. It is also worth thinking through what happens under fault conditions, so for example what is the implication of losing the lights should you trip the power circuit with a power tool etc.

[Andy Hall]

I think it's perhaps as broad as it is long.

My starting point was a garage with single brick walls and pillars at the front and periodically along the sides. I installed stud frames next to the walls except at the pillars using a gap of about 25 mm behind. I put 50mm Celotex in the frames and taped them with foil tape. I then applied 18mm ply across the whole lot. Where the pillars are, there is just a gap behind the ply. This doesn't make the garage any narrower from the perspective of getting a car in if I ever wanted to do so since the width is limited by the pillars at the front. The other advantage of this approach is that I can fit things to the walls anywhere without having to tit around with plugs. For anything heavy like my dust extractor, I can screw to the studs.

The double cavity wall approach would achieve virtually the same thing, I think. You could compare the insulating properties of each, but I don't think that there's a great deal in it since the insulating material is the main determining factor.

Fixing things involves plugs each time unless you do something like I've done in the past. That is to fit Spur shelving rails at intervals along the wall for most of the height of the wall. You can then easily put shelves in and move as needed. Near the top of the wall you can install a French cleat. This is basically a piece of timber - e.g. about 70x35mm with a sloping edge at the top. It slopes back towards the wall. You fit similar pieces the other way round to the backs of cupboards, boards to hang tools on and so on. A spacer piece of similar depth is attached to the bottom of the cupboard/board The items can then be moved around as needed.

I've been researching these to do a swap when it's warmer. The ones by Henderson et al. are much of a muchness and I was not impressed with the quality. Plus, I don't care much for the roller slatted look which strikes me as rather industrial looking.

I'm gravitating towards sectional doors at present as being a better compromise between functionality and aesthetics.

In terms of manufacturers, Hormann seem to have a much better quality than the others, but the price reflects that. If I went with that, I would probably attach Celotex to the inside as I have with the current (up/over) doors.

Can't help you with that one. The floor was already there and I wasn't about to dig it up. I did do the calculations of heat loss, and provided that the walls and roof are insulated, it isn't a great deal - possibly 1kW or so on this size. I never have cold feet when I'm working out there, although I do have some anti-fatigue mats to stand on as concrete does get hard after a while. It also helps if you drop anything.

Yes. I already had a pitched and trussed roof - felted and battened same as a house. The storage space is very useful. I fitted 50mm Celotex across the tops of the rafters leaving the depth of them to provide ventilation. I suppose I could have fitted 25mm between rafters and 25mm over the top but it wasn't worth it. I used long drywall screws with large flat washers and screwed through the Celotex into the rafters. Gaps were taped. It's arranged that the space behind the Celotex connects with the space behind the wall framing. I then put in soffit vents between each pair of rafters to ensure ventilation. The joists were then boarded throughout apart from between one pair where a wooden loft ladder is fitted for access . Behind it is a large removable panel in the floor that provides access to hoist large but not heavy items up and down. I installed an electric hoist above the hatch for the purpose.

Not insulating the "ceiling" is deliberate. Usually the ladder and access trap doors are closed which keeps heat below that level rather than letting too much warm air convect into the roof space. However, it does mean that there is some warmth and than is sufficient to prevent metal items from rusting etc.

My only comment here is to allow for plenty. SWA cable is cheap. Digging trenches is a pain in the botty.

I put in three compartment trunking around the walls and have run wiring in PVC singles rather than T&E. Circuits are wired as radials with one circuit per side. I then have individual 16 and 32A circuits with IEC 60309 outlets for machinery.

Lighting circuits run in conduits to fluorescent fittings with electronic ballasts in rows and intervals across the ceiling.

Consumer units are cheap so I put in large ones to accommodate all the circuit breakers.

I felt that I would rather adopt this approach to make later changes easier.

[Guy King]

The message from John Rumm contains these words:

After all, that's only the same as two of me standing close together.

[Ian White]

Which moves us on to the missing part of the OP's question: what about the windows?

If the walls, floor and roof have been insulated, and the door draught-proofed, what would then be a reasonable standard and size of windows for a combined garage/workshop?

I have the same problem coming up here, and am finding it hard to decide between:

1. Shelling out for new PVC DG units... but it's only a wooden workshop, so that option could easily go OTT in terms of cost. Where *is* the absolute cheapest end of the market in new windows, anyway?
2. Trawling the local DG suppliers for mis-measured units they want to get rid of. Not much luck there, so far - all the ones available locally are proportioned for houses, and would look daft in a low, single-storey workshop.
3. Using new or reclaimed sealed glazing units in wooden frames... storing up repair/replacement work for later?

[John Rumm]

Option 4 (which worked for me) visit local reclamation yard and pick up a complete DG window with frame for 20 quid.

[Christian McArdle]

The latter. Build a studwork frame inside the brick outer. Fill frame with Kingspan. Line with 12mm WBP ply. This means you can screw and mount things really easily. If you feel you might convert the garage into habitable space in the future, put some additional insulation in front of the studs as well.

Kingspan again. Use breathable membrane under the tiles and wedge Kingspan right up to the surface. Better still, insulate between and above the rafters.

Yes. Run at least a 32A circuit to the garage.

Christian.

[Ian White]

Sorry, I should have mentioned that one too. The local DG makers are happy for me to go skip-diving, but out here in the country we're still decades away from replacing old DG.

Reclamation yards are something they have around cities, aren't they? Around here, decent building materials aren't left lying around - they're more likely to vanish before you can even blink. (This whole house was built from top-quality materials, courtesy of king and country. When the troops marched out of the army camp in 1946, the locals marched in and recycled the whole place as a service to the environment.)

[zymurgy]

I've just had my old DG replaced, and kept all of the sealed units.

I now have the luxury of triple glazing (as I kept the originals and bolted the new into the recess) in my humble workshop ;-)

Cheers

Paul.

[Steve Walker]

And the pitched frame provides excellent storage for all those lengths of timber, moulding, pipe, ladders, etc.

[Roger Mills (aka Set Square)]

Yes, I'm planning on having a decent window on one side - which I previously omitted to mention. The other side is close to a row of leylandii, and the back is close to the site boundary, facing a public footpath. I suppose I could have some skylights?!

[Roger Mills (aka Set Square)]

The builder that I'm likely to use sometimes has second-hand windows which he has removed from other jobs when doing extensions etc., so that is another possibility.

[Roger Mills (aka Set Square)]

How about blockwork, and then clad *that* with plywood?

Could I simply use a heavy wire mesh, rather than individual bars? What depth of screed would be needed to prevent it cracking under point loads?

A pitched roof with insulation immediately under the tiles sound good - so that the storgae space is on the 'warm' side of the insulation.

Not sure that 2-Jags would see it that way!

It will be 7 or 8 metres from the house. I'd probably use a couple of fan heaters on the odd occasions when I was working in cold weather. I'm not proposing to use any tools which need more than a 13a plug each - drills, circular saw, hand-held power planer, etc.

The minimum requirement is for lighting, and power for the door. I *could* run an extension lead from the house for the tools - but it would be much better to have permanent power in there.

[Roger Mills (aka Set Square)]

Not quite sure what you mean. What do they look like?

Near the top of the

Now that's a really good idea!

I'm not quite sure what is meant by the term 'sectional' in this context. How do they fold, or whatever, and where do they go to when open?

That seems like the way to go. Many thanks.

[Roger Mills (aka Set Square)]

Many thanks for your thoughts.

[Owain]

Skylights let in a disproportionate amount of light for their size, and have the advantage that scrotes can't easily look in and see what's worth nicking.

You can also open them to let the smoke out if Mary comes visiting :-)

Owain

[Andy Hall]

They are steel rails with regular slots. There are then U-shaped brackets to fit them.

e.g. Screwfix 16003 17905 etc.

Different heights of rail and lengths of bracket are available.

This is a clone of the original Spur Steel-Lok product

one is readily available, but it's worth shopping around for price.

Google using "french cleat" and you will get some illustrations of different ways to do this.

They take virtually an L-shaped path because that's how the rails run. When open, the door would end up horizontal, immediately under the ceiling joists rather than at the level of the top of the door as an up/over door does.

With my present arrangement of up/over doors, I use the space between the top of the door and the ceiling (about 300mm) as a space to store timber. When the door is changed, it will go above this rack and below the ceiling.

Since the sectional doors are following an L-shaped path, it means that you can put taller things closer to the doors as well.

Here is an illustration

on product, these are in the £4k area.

The other consideration is if you want to go for a single, full width door. You will find that there is very little around in the entry level up/over doors (e.g. Henderson, Cardale, ...) that will go to the full width you intend. That was one of my reasons, apart from build quality, for looking at Hoermann. It's worth going to a specialist place and looking at different ones before you decide. Bear in mind that lead times are often 6-8 weeks.

Another good quality product is Silvelox. This is from an Italian manufacturer

are a lot more customisation options and they are a bit better than Hoermann, but cost about 50% more.

I did look at roller shutter doors. From a functionality perspective, they are good in the sense that they roll into a cassette typically. You can also get them with insulating material on the back. Normally the slats are steel or aluminium, sometimes plastic covered. As I mentioned, although the functionality is attractive, I don't particularly like the appearance and it wouldn't really go with the house either.

Since you are having to go for planning permission you can do this.

There is a planning exemption for roof heights to apex of 4m, but I believe that having it a brick built building makes it permanent and therefore not exempt.

The storage space is definitely worth having. Perhaps it might be an idea to do a mockup against a photo of the house using a drawing package and make sure that the larger roof doesn't make it loom....