# Workshop Design/build advice - insulation



## Hobbyshop (28 Nov 2009)

Hi to everyone.

I am a complete newbie here, though I have spent a lot of time reading through the forums and learning a great deal.
It's a great site, particularly for someone like me who has very limited experience in woodworking anyway.

Any woodwork I have done to date has been done with a small range of power tools and hand tools in my detached garage, which is approximately 26ft x 12 ft, cold and a bit damp, and usually houses the car.

Now I have retired I have more time for hobbies and I am lucky enough to be able to add a workshop extension to the garage.

I have almost completed the drawings for the planning application and the workshop area will be approximately 300 sq. ft. in total.

I have decided the construction will be single skin block walls on strip foundations, with a concrete tiled pitched roof to blend the whole thing in with my bungalow. The walls will be pebble dash rendered externally.

I intend to have underfloor insulation installed (probably 4" expanded polystyrene), and I will have the roof insulated at rafter level. Not sure what thickness I should specify.

I was thinking of insulating the walls with 50mm Celotex (or equivalent) between battens with a plasterboard finish. But I am wondering whether I could get away without insulating the walls. It's already looking expensive, but I don't want to skimp on the insulation if it is important.

I had a visit from the Building Surveyor from the local council this week to discuss the requirement for Building Regulations approval, and he was very helpful, but since it is a workshop he doesn't really care whether I insulate it or not. 

My aim is to have a damp-free environment that I can keep at a reasonable temperature for working in throughout the year, and so that tools don't rust as quickly as they do in my garage.

I would very much appreciate your thoughts and experiences about levels of insulation. I know there are lots of threads about these issues already, but I find they get a bit confusing as they all relate to slightly different construction types.

So, if you were building something along the lines I have described, what sort of insulation would you be installing?

Thanks in anticipation.


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## MikeG. (28 Nov 2009)

Hello Kevin and welcome.

My strong advice would be to build a timber frame workshop and include the insulation within the framework, rather than waste 100mm all round by using block. The building can look identical, with the same external finish as the way you propose, but would benefit from being so much warmer, and the construction costs will be much reduced. Insulation is an absolute must.

I would also advise against plasterboard in a workshop. Some people can get on with it, but you are limited to where you can make fixings to it, it is terribly fragile in a working environment, and can go horribly mouldy and soggy in a cool damp environment.

Mike


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## Hobbyshop (28 Nov 2009)

Thanks for the comment Mike.

I hadn't even considered a timber frame construction. the garage it will attach to is a concrete block construction and I automatically went that route. A good lesson in the usefulness of a bit of lateral thinking.  

You are absolutely right about maximising space of course and while I know nothing at all about timber frame construction I will definitely be looking into it.

The comment about the plasterboard is something that was already worrying me and was part of the reason for thinking about leaving out the insulation so I could fix direct to the blocks.
But then your comment that the insulation is "an absolute must" suggests that wasn't a good idea.  

Thanks for te advice.


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## MikeG. (28 Nov 2009)

I have posted so many times over this next point, Kevin, that people all over the country are rolling their eyes and saying "here we go again", but a critical part of the design of a timber framed building is a masonry plinth. It should be built on a brick plinth that finishes at least 2 courses above ground level. This will make all the difference to the longevity of the building, and, quite likely, is a detail you will find on your house and/or garage. Render shouldn't extend below a damp course.

I would also conside a raft foundation rather than a strip footing. A lightweight building on a raft can work well, and save quite a bit of money. If you want a timber floor (I don't, but some do), you can do a floating floor on top of the concrete slab.

Mike


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## Hobbyshop (28 Nov 2009)

Hi Mike

So would that mean a reinforced raft to ground level with a minimum 2 courses of brickwork around it, then a damp-course with the floor finish cast inside the bricks? I was not looking for a wooden floor, but can I still install the expanded polystyrene insulation under the floor?

There is a small amount of settlement at one corner of the existing garage base, which I was going to get underpinned and was leading me towards the strip foundations. To be fair the building surveyor who visited did also suggest a raft as a possible option.

For the bog-standard block construction I was happy to do the layout drawings myself and use the Council's building surveyor and a reputable builder to ensure the construction quality was right. I am thinking that if I go for timber frame construction it is probably best for me to use an architect to get the design right (roof loads etc.). 
Any thoughts on that.


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## MikeG. (29 Nov 2009)

Kevin,

well, you could do the floor that way, but I would suggest putting a float finish on the slab and having that as the floor. You can cast it on top of insulation if you wish. Key to success here is to make sure that the slab is cast about 50mm above the highest point of the finished ground level outside the building. That will give the edges of the slab a chance to dry out, and with a DPM under the slab you should have a nice dry floor.

The roof will be no different from a timber frame building than for a block one. If you are going to have trusses made, then the manufacturer does the calcs for you. If you are going to do a cut roof (ie hand-made on site), then let me know and I can give you the timber sizes.

This next point is very important. You may not require building regs approval for this building. See this thread https://www.ukworkshop.co.uk/forums/viewtopic.php?p=431423&highlight=#431423. If the floor area is 30 sq.m or less, the building is a metre or more from a boundary, and it is of non-combustible material (rendered is fine for this), then you wont need Building Regs approval. You could build the roof out of spaghetti if you wanted......

Mike


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## squib (29 Nov 2009)

Insulation seconds.I know they are a little far away from you but i know people from cornwall who saved money using these guys.I have bought off them and their prices are good,many of the boards just have edge damage or tears on the paper outer etc.

http://www.secondsandco.co.uk


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## Hobbyshop (29 Nov 2009)

Thanks Mike

That is a very generous offer on the sizes for the roof timber.

With regard to the building Regs., I got one of the Building surveyors from the local council to come out and take a look over my plans to get some advice.
His view is that I will need to apply for Building Regs approval (though he would say that wouldn't he. :roll: ).
The new construction is borderline on the size limit (about 29.5 Sq.Metres), and it does get to within a metre of the boundary, but would probably fit the criteria with regard to non-combustible material.
I think the main issue though is that it is an extension of an existing outbuilding which will also be modified (mainly the roof) and the total area of the complete structure will be almost 60 Sq. Metres.

The only issue I have with the Building Regs thing is that it adds cost. Our local building surveyor is very helpful and having them do the inspection would give me added confidence that the builder's standards were suitable.
I won't be doing a self-build as I have no real experience in this area and I would like to get the shop up and running fairly quickly.

Building Regs requirements shouldn't cause any delay. The surveyor just advised me to get a builder organised and give hem a ring once we had got the footings dug out, and he would come along to do the inspection and bring the paperwork for the application at the same time.

I have googled for Timber Frame information and there is a company local to me who do the design, manufacture and construction (if required) for timber frame buildings. This may be too small to interest them, but I think I will call into their offices and have a chat anyway, and see what I can learn.

Hi Squib - Thanks for the link. I will take a look.


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## MikeG. (29 Nov 2009)

Don't go down the road of getting a timber frame manufacturer involved. This is way too small for them, and every single builder in Britain can knock together a bit of stud walling. If you send me a PM in the week I'll do a quick sketch of the wall build-up by email, and with your floorplan and some roof timber sizes that should be enough for a builder to give you a price. 

The only bit the concerns me is that you say it is really an extension. Not only does this bring it under building regs, but it also means that you will have to use the same foundation type as the building you are extending..........you won't be able to build on a raft if you are joing to a building with strip footings. This will bump up your costs a bit. Have you considered seperate buildings?

Mike


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## Hobbyshop (29 Nov 2009)

Thanks for all the help Mike

I will put together a PM in the next couple of days. If I can attach a couple of image files showing more info about my plans I will.

The existing building that I will be extending is a detached garage and it is single skin blockwork on a concrete raft (so shouldn't be a problem with putting the extension on a raft too by the sound of it.

The garage has a flat roof at the moment and I want to change to a pitched roof to improve the general appearance while I am getting the workshop done.

Thanks again for the offer of help. I'll get something off to you when I can.


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