Building a garage & gym - wall options & costs

[RobM77]

We've just had planning permission granted for a combined double garage and gym. The whole structure is 13.5m long and 6.3m wide (85m^2), with the garage taking up 7.5m of the length and the gym the other 6m.

Does anyone have any suggestions for wall construction? Obviously we'll be asking the opinions of the builders who quote for us and the planners, but I'm keen to hear from people with experience of living with a garage. I'm assuming that our basic choices are single blockwork, cavity wall (block & brick) or insulated blocks, and then plasterboard or external wall insulation options on top of that. All I can seem to find on the web are pleas from people with cold and damp garages wanting to improve them, rather than advice for someone starting from scratch. The outside will just be rendered to match our house, so no worries there about having attractive bricks on the outer layer etc.

The garage will be for keeping cars that don't weather outside. I currently have a 2-Eleven (open, so no roof or windows etc) and will hopefully keep a single seater in there in the future. I'll also want to be able to work in the garage all year round without the frozen fingers I've traditionally associated with garages in winter. The gym is also for all year round use, although mainly in winter.

For costs I've heard estimates from as little as £200 per square metre right up to £700 per square metre, so I'm assuming that the above options vary wildly in cost?

Any thoughts or experiences much appreciated - thanks.

[Snake the Sniper]

My garage was built with 140mm blocks, then a 100mm airgap, then 100mm rigid insulation fitted into the stud walling, then topped with 18mm ply. The outside was then rendered. The walls keep the place at a nice even temperature, but I wish I'd gone for greater under-slab insulation as the floor can get damp when I turn my little 2Kw fan heater on. Having some form of permanent heating would resolve this, but mine's only a 7.5M x 3.5M workshop, so it would be a waste of money to heat it.

[toohuge]

All too often people build their garages at lower insulation standards than their main living space - thinking it will save on the construction costs. In reality, the initial costs are not that much lower. It just leads to cold fingers and usually abandoned spaces in the winter / really hot spaces in the summer.

I cannot comment on the price difference as I am based in the US, so different wall systems will have different costs, however...

Under slab insulation is a good option to look into - however I am concerned about the rigid foam insulation used as I do not think we have seen it in use long enough to understand how / if it degrades, what the consequences are for your floor. Having said that, I have not heard of any issues if used correctly.

As for wall systems.... I would look at insulated concrete foams. Given you will be building a relatively simple shape, these can be installed and poured very quickly - if using an experienced crew. This will give you good thermal performance and a strong envelope.

Remember though, you wall system and slab insulation will be almost irrelevant if you have a poorly performing garage door - these are massively over looked and can be expensive, however this one component can make or break your whole building performance.

Chris

[toohuge]

All too often people build their garages at lower insulation standards than their main living space - thinking it will save on the construction costs. In reality, the initial costs are not that much lower. It just leads to cold fingers and usually abandoned spaces in the winter / really hot spaces in the summer.

I cannot comment on the price difference as I am based in the US, so different wall systems will have different costs, however...

Under slab insulation is a good option to look into - however I am concerned about the rigid foam insulation used as I do not think we have seen it in use long enough to understand how / if it degrades, what the consequences are for your floor. Having said that, I have not heard of any issues if used correctly.

As for wall systems.... I would look at insulated concrete foams. Given you will be building a relatively simple shape, these can be installed and poured very quickly - if using an experienced crew. This will give you good thermal performance and a strong envelope.

Remember though, you wall system and slab insulation will be almost irrelevant if you have a poorly performing garage door - these are massively over looked and can be expensive, however this one component can make or break your whole building performance.

Chris

[RobM77]

Thanks for the suggestions. We'll definitely be going for something under the floor. Good point on the doors too, I hadn't thought about that. For the walls we're tight on space inside and out, although obviously it's pointless having space if it's too cold to use, but I think this might rule out a proper cavity wall. We're currently considering insulated blocks and insulating plasterboard inside - the outside will be rendered. Hopefully that'll be enough?

[FlashmanChop]

Assuming it is of brick construction I would go for a beam and block type ground floor buildup, using a plasmor block (aglite) and the same 100mm block in the walls, 80mm cavity, including 50mm ecotherm and brick outer skin. Same block means you are not messing about with different blocks on site

[RobM77]

FlashmanChop said:

Assuming it is of brick construction I would go for a beam and block type ground floor buildup, using a plasmor block (aglite) and the same 100mm block in the walls, 80mm cavity, including 50mm ecotherm and brick outer skin. Same block means you are not messing about with different blocks on site

Thanks. Currently we're down for a single skin of concrete blocks rendered, so no cavity...

[fergus]

I've got the following, which I built 3 years ago and seems to work well:

10m x 6m garage

- twin skin 100mm blockwork with 100mm gap with cavity bats fitted, external render
- fire door for personnel door
- double glazed window at one end
- hormann 50mm insulated sectional door at the other end
- 200mm deep roof joists packed with 200mm rockwool insulation with a chipboard floor on top of that (garage attic floor). Plasterboard ceiling to main garage

The floor however, due to building regs (built near large tress and on clay), is a complicated slab with a LOT of rebar and mesh in it. The main slab is 250mm thick, which doesn't have any insulation in it. Due to the sheer size of this, the thermal mass remains fairly constant. Initially I used to get some condensation on the floor when the humidity levels were high, but now run a Meaco DD8L humidifier all the time on "eco" mode, which leaves me with a bone dry, warm garage.

- with a natural slate roof, the whole project cost me around £23k, including groundworks, foundations, blockwork, timber, slates and doors. I did the roof joists/timberwork and all the groundwork myself though...

Although the missus has said that my paternity leave shouldn't have been spent building the roof...

It's worth considering EWI, external wall insulation. This is how a lot of commercial buildings are built, especially in Europe. It's much cheaper and quicker than messing around with UK techniques and can offer far better thermal performance, especially if you go for something like 100mm thick options. Factor in your ventilation options for the gym end of the garage, to avoid vapour related dampness.

Edited by fergus on Tuesday 27th January 10:43

[RobM77]

Thanks Fergus. I'm beginning to wonder if we should have cavity walls judging by your post, others, and the research I've done so far. I haven't got down to doing the thermal calculations yet, but I'm wondering if I should.

Incidentally, your garage works out at £383/m^2, which is pretty decent. I could do much of the work myself too, but I earn more per day than a builder charges and don't get annual leave (or paternity leave!), so it would probably make sense for me to go to work instead, although I could leave finishing touches for me to do at the weekends, such as flooring or even the plasterboarding and interior insulation.

[Mark Benson]

Have you considered SIPS for the walls? Seems to me that they'll give you all the insulation you'll need and be as narrow as a single skin of blockwork.

[RobM77]

Mark Benson said:

Have you considered SIPS for the walls? Seems to me that they'll give you all the insulation you'll need and be as narrow as a single skin of blockwork.

No, but thanks, I shall research them now.

[RobM77]

Thanks for all your thoughts. I've found a U value calculator online and done some research on the thermal properties of various materials, along with their cost and thickness. I've come up with the following wall construction, listed from inside to outside:

Standard Plasterboard 12.5mm (U=0.14)
Celotex Board 25mm (U=0.02)
Thermal concrete block 100mm (U = 0.13)
Render 20mm (U = 0.73)
U = 0.43 W/m^2K (comparable to a house, which is more than good enough for what I need).
Total wall thickness: 157.5mm

We'll also add something under the floor and ensure that our garage doors are decent, so thanks for your thoughts on those (they're going to be quite large doors, so insulation of those will be very important).

[Happy Jim]

RobM77 said:

Thanks for all your thoughts. I've found a U value calculator online and done some research on the thermal properties of various materials, along with their cost and thickness. I've come up with the following wall construction, listed from inside to outside:

Standard Plasterboard 12.5mm (U=0.14)
Celotex Board 25mm (U=0.02)
Thermal concrete block 100mm (U = 0.13)
Render 20mm (U = 0.73)
U = 0.43 W/m^2K (comparable to a house, which is more than good enough for what I need).
Total wall thickness: 157.5mm

We'll also add something under the floor and ensure that our garage doors are decent, so thanks for your thoughts on those (they're going to be quite large doors, so insulation of those will be very important).

If that really is comparable to a house then all houses would be built like that - if you are OK with that then great. If it was my choice I'd go standard cavity wall or if feeling brave then SIPs plus external insulation cladding (as in Europe).

Rgds

Jim

[RobM77]

Happy Jim said:

RobM77 said:

Thanks for all your thoughts. I've found a U value calculator online and done some research on the thermal properties of various materials, along with their cost and thickness. I've come up with the following wall construction, listed from inside to outside:

Standard Plasterboard 12.5mm (U=0.14)
Celotex Board 25mm (U=0.02)
Thermal concrete block 100mm (U = 0.13)
Render 20mm (U = 0.73)
U = 0.43 W/m^2K (comparable to a house, which is more than good enough for what I need).
Total wall thickness: 157.5mm

We'll also add something under the floor and ensure that our garage doors are decent, so thanks for your thoughts on those (they're going to be quite large doors, so insulation of those will be very important).

If that really is comparable to a house then all houses would be built like that - if you are OK with that then great. If it was my choice I'd go standard cavity wall or if feeling brave then SIPs plus external insulation cladding (as in Europe).

Rgds

Jim

We don't really have the room for a cavity wall, thus the original question. Sorry, I probably wasn't clear enough when I said 'comparable to a house'; what I meant was that building regs state a maximum of 0.35 for a house now, and period stone houses are around 0.9 to 1.0 (I found a study of period homes in Scotland yesterday), so we'd be in the ballpark for thermal insulation alone. A modern home with cavity walls will probably comfortably exceed 0.35 for thermal insulation, and yes of course, that wouldn't be viable to achieve with a single layer of blockwork (you'd end up with a total wall width wider than a cavity wall, plus it would cost a huge amount more), plus there's damp levels to consider and other considerations that result in the standard modern construction methods for homes.

[anonymous-user]

For a free standing garage, I think that going all out on insulating the walls will be a bit pointless when you add a huge great garage door, that, even if you go for a well insulated and fitted one, will always be a weak point. Particularly if you actually want to open it occasionally!

[RobM77]

Inkyfingers said:

For a free standing garage, I think that going all out on insulating the walls will be a bit pointless when you add a huge great garage door, that, even if you go for a well insulated and fitted one, will always be a weak point. Particularly if you actually want to open it occasionally!

It's a very valid point, which is why I asked the question in the first place rather than just relying on the U values; I'm interested in people's experiences with living with a garage.

What my Dad's done to get round this problem is to make a seperate workshop section to his garage, so he's built a stud wall right behind where the cars go with a decent door for access. I used to work on my racing cars in the garage bit (single skinned brickwork) and it was horrible in the middle of winter. I used his workshop bit for engine rebuilds and even on a winter's day it was quite comfortable with just a single skin of standard house bricks and a 20mm gap to standard plasterboard, plus a couple of small heaters of course. I'd like to recreate his environment with two large garage doors, which is obviously a tricky thing to plan for on paper! The blockwork and render construction is a given, because blockwork is cheap and render matches the house, and I thought adding the insulating foam board behind plasterboard on the inside would be a nice touch for not much loss of interior space. The option is a cavity, but I'm worried about the space it'll take up.

[TA14]

Why is the wall width so critical on a 6.3m wide garage?

[RobM77]

TA14 said:

Why is the wall width so critical on a 6.3m wide garage?

I wouldn't say it's critical, but my parents' garage was 6m wide and it really wound me up with the lack of space down the sides of the cars for jacking and working on hubs, brakes etc.

[TA14]

RobM77 said:

TA14 said:

Why is the wall width so critical on a 6.3m wide garage?

I wouldn't say it's critical, but my parents' garage was 6m wide and it really wound me up with the lack of space down the sides of the cars for jacking and working on hubs, brakes etc.

FWIW I don't think that it's worth the bother of trying to gain 200mm width and you might as well build cavity walls. When working on the cars if they are parked awkwardly you can use dollies to move them to give enough room. Lengthways you'll need two expansion joints - these are a lot easier to detail for a cavity wall than a single leaf with wind posts unless you go for a halfwayhouse set up with piers. SIPS might give you all that you want http://www.wbs-ltd.co.uk/wp-content/uploads/2012/0... for thickness and insulation. I wouldn't want plasterboard in a garage.

[VxDuncan]

Don't forget at that size you have to comply with building regs, so there will be minimum standards of construction to comply. From memory, insulation requirements ramp up dramatically if there's a permanent source of heating or cooling to be installed, in which case it pretty much has to comply with new build requirements.

Have a good dig round the planning portal.

Couple of other things - if you build with a good big cavity you can convert to living space later easily BUT you neighbours might thing you are building more accommodation in the garden. Happened to a neighbour of mine and caused him a world of trouble.

Another thing to consider is the practicality of the finished space. Personally I'm so glad I built with solid concrete blocks as they are very strong and easy to hang heavy things like garage shelves off. Thermolites aren't. Down side is massive thermal mass if you are trying to heat them.