Richards Garage/Workshop build

[Richard39]

I've read all of Mike Gs thread, and others on here regarding workshop builds, and the information contained within is amazing. I've had mental plans for a timber garage for a couple of years, and I finally had a concrete slab put down a few months ago to try to move the idea from my head to reality . I searched high and low on the net for any form of plans to work from, but I finally gave up and started researching different elements of the build instead. That brought me to this mine of information, which is exactly the sort of thing I was after in the first place.

I really like the plinth detail that removes the large overhang of timber that would result from a single row of bricks. I had an idea for a slight change to the third course of bricks, and that is to replace it with a course of plinth stretcher bricks. This would remove the need to install wedges under the bottom board as it would sit naturally in the recess created by the plinth stretcher brick, and any rain would just wash straight down the bricks. Can anyone think of a reason to not do this way?

[Andyp]

Hi Richard and welcome to the forum. As you have seen there are plenty of very knowledgeable folk around here who I am sure will be along in a while to answer your query.

It might be better if I move this post into it's own thread that way you can add some photos as your build progresses. You will need to create a couple of more posts for the spam trap goes away.

[Mike G]

.......I had an idea for a slight change to the third course of bricks, and that is to replace it with a course of plinth stretcher bricks. This would remove the need to install wedges under the bottom board as it would sit naturally in the recess created by the plinth stretcher brick, and any rain would just wash straight down the bricks. Can anyone think of a reason to not do this way?

Welcome to the forum, Richard.

I do this all the time with houses. It's a great detail. However, it isn't cheap, and it can look a little over-blown on a shed. However, if you are so inclined then just do it. You may find that with the remnants of the brick shortage, and the incredible amount of building going on at the moment, that getting hold of some plinth stretchers in your chosen brick-type isn't easy at all. I couldn't for my house, and ended up having a brick cutting company cut some for me from ordinary bricks, and then glue the brick dust back on the cut face to disguise it. It sounds terrible, but the result is indistinguishable from an orthodox plinth brick.

[Richard39]

Thanks for the heads up Mike. The idea of plinth stretchers only came to me in the last few days, and I hadn't even considered cost or availability yet, so I'll have to look into it locally. A quick google suggests they are available for around £2 a brick, which in the great scheme of things isn't a huge number. The garage will be 7M x 4M approx, so it's a little bit more than tuppence halfpenny to build anyway

[Richard39]

Hi Richard and welcome to the forum. As you have seen there are plenty of very knowledgeable folk around here who I am sure will be along in a while to answer your query.

It might be better if I move this post into it's own thread that way you can add some photos as your build progresses. You will need to create a couple of more posts for the spam trap goes away.

Thanks Andy. Not much to see at the moment other than a concrete slab, but I'm sure I'll have photos of real interest before long.

[9fingers]

Richard, welcome to the forum. With three posts under your belt now, the annoying anti-spam measures go away and your inputs will be posted immediately without manual intervention.

Bob

[TrimTheKing]

Hi Richard and welcome aboard.

Lots of builds going on at the moment and more to come soon, hopefully...so look forward to seeing yours progress.

Cheers
Mark

[Richard39]

I'm thinking ahead a bit to my roof construction. I will be wanting to use the roof space for storage of miscellaneous items. Probably more bulky rather than heavy items, but I've no wish to under engineer it. The primary purpose of the building is a garage, with enough space to use it as a general workshop as well. It is being built under permitted development, and won't need building regs approval. As my concrete slab is 100mm above the surrounding ground level, my eaves height is restricted to 2.4m, and ridge height 3.9m. I'm going for close to maximum size, so the internal size of the garage will be 6.9m x 4.2m. I'm not sure what design of roof would work best. I don't really want a huge structural ridge, but I'm not sure what size joists I would need to go for otherwise. Anything big could eat into my headroom and make the building feel quite small inside. I'm just not sure how to go about coming up with a suitable roof design. It is probably worth mentioning that as it's a garage one of the gable ends is going to have a 2.5 x 2m opening for a sectional garage door, which I'd imagine could need a reasonable size lintel if the gabel end is needed to support the roof. Does anybody have any thoughts how to attack this?

[9fingers]

With the heights you mention, you could fit joists at wall plate level and these would be 2.3m above the floor. Identical to most housing. these would be in tension from a roof formed of a pair of rafters per joist and only needs a modest ridge board. Depending on roof cladding and rafter length, these could be at 400 or 600 centres.
At the ridge I guestimate you would have about 500mm between ridge and joist tops. Allowing for a clear access space you could still store quite a lot up there. A huge number of 400mm cube cardboard boxes almost out the to walls. Insulation on the underside of the roof should keep you warmer/cooler according to season.

This style of roof puts minimal load onto gable walls and so the lintel over the garage door becomes little more than a catnic - subject to calculations!

With one or two of your adjacent rafters doubled up and a pair of acrows temporarily added would support a block to take out an engine etc if needed.

HTH

Bob

[Richard39]

With the heights you mention, you could fit joists at wall plate level and these would be 2.3m above the floor. Identical to most housing. these would be in tension from a roof formed of a pair of rafters per joist and only needs a modest ridge board. Depending on roof cladding and rafter length, these could be at 400 or 600 centres.

I'd imagine that I would end up with the internal height somewhat lower than 2.3m, as that is the limit for my external eaves height? I suppose it would depend on the size of the joist as to how much lower this would be. With just over a 4m span, these might be quite chunky? This is where I'm not sure what size joist would be ideal/needed.

This style of roof puts minimal load onto gable walls and so the lintel over the garage door becomes little more than a catnic - subject to calculations!

That's part of my thinking against a structural ridge, but then I'm hoping for some magic formula to let me have my cake and eat it with regards to space. We can but dream .

With one or two of your adjacent rafters doubled up and a pair of acrows temporarily added would support a block to take out an engine etc if needed.

I'm well covered in that regard. I've got an engine crane and a power floated slab. Getting an engine out will be a doddle .

Thanks for your help. It's appreciated.

[Dan0741]

Richard Welcome to the forum, you join the ranks of a fair number of self builders! Your project sounds interesting, I know you said its just a slab, but photos inform and seem to make the wheels turn here, see if you can get some posted as soon as you are able.

All the best

Dan

[9fingers]

I'm not sure about the exact definition of "eaves height" It would be normal for the soffit and fascia to be below wall plate level and the tiles/slates would come down to part way down the fascia board to meet the gutter.
One approach might to ask the local planners how they would define it but you might not like the answer. The other approach would be draw a section through the roof edge, fascia etc and pick a mid line as the nominal height and prepare your argument should anyone challenge you. Provided the rest of your design is clearly compliant and they don't think you are pushing your luck on every parameter they would be incredibly miserable to argue on eaves height.
Mike G might have an expert view?
Bob

[Richard39]

Unfortunately they aren't so generous when it comes to measuring eaves height in respect of permitted development. Taken from some Government technical guidance "Eaves height is measured from ground level at the base of the outside wall to the point where that wall would meet the upper surface of the roof slope - the overhang should be ignored for the purposes of measurement" This is the source of my eaves height anxiety with regards to joist sizing. Bigger joists pushes the roof level up, so the wall plate height would need to be lowered to allow for this, unless I'm missing a trick?

[Richard39]

Richard Welcome to the forum, you join the ranks of a fair number of self builders! Your project sounds interesting, I know you said its just a slab, but photos inform and seem to make the wheels turn here, see if you can get some posted as soon as you are able.

All the best

Dan

This is true, there's nothing like a photo to get the creative juices flowing So, the slab is currently looking like this:

[9fingers]

I reckon with a bit of cunning you could get the eaves height to be a small fraction of the joist height added to your wall plate level by knocking off the top corner of the joist and the thinnest of fibre cement slates.

From the point of view of the roof alone, the rafters are in tension and so don't need to be very high. The rafter bear onto the wall plate. The problem comes from the storage requirement which put an imposed load on the the rafters. Could you contemplate any support pillars under your storage area? It would possibly give you another 100mm headroom all over.

Bob

[Dan0741]

I am so envious. My slab is about 30m from the nearest place I can get with a vehicle, every block, brick, slate and all the wood has been carried piece by piece up the garden.. That will save you a considerable amount of time!

[9fingers]

A quick sketch of what I'm thinking of



Bob

[Mike G]

.....From the point of view of the roof alone, the rafters are in tension and so don't need to be very high. The rafter bear onto the wall plate. The problem comes from the storage requirement which put an imposed load on the the rafters. Could you contemplate any support pillars under your storage area? It would possibly give you another 100mm headroom all over.

Bob

Could you just explain this a bit Bob, please? Rafters are in compression in a simple truss, with the tie (bottom chord/ joist) being in tension. I can't see how anything stored on the joists imposes a load on the rafters.

If the joists are struggling with storage loads, then hangers are the traditional solution: a tensile member hanging down from the ridge board at every (say) 3rd rafter, bolted to a rafter and the joists, with a binder alongside on the top of the joists to ensure that they all act together rather than deflecting individually.

[Richard39]

I reckon with a bit of cunning you could get the eaves height to be a small fraction of the joist height added to your wall plate level by knocking off the top corner of the joist and the thinnest of fibre cement slates.

From the point of view of the roof alone, the rafters are in tension and so don't need to be very high. The rafter bear onto the wall plate. The problem comes from the storage requirement which put an imposed load on the the rafters. Could you contemplate any support pillars under your storage area? It would possibly give you another 100mm headroom all over.

Bob

Cutting the corner off the joist would definitely have to be part of any strategy to maximise internal space. I'm not sure how thin I could without reducing the strength of the joist, or am I misunderstanding how the load is distributed in the roof?

I think if it came to it I would sacrifice the storage over installing support pillars. After years of making do in the space offered by a single garage, I'm looking forward to being able to move freely around a car.

[Mike G]

Hi Richard, and welcome.

Your joists need to be 220 x 45/50 at 400 centres for that span, if they are to take a load (storage above). I suggest leaving an access door in the gable so that you can feed long lengths of stuff in. You shouldn't really be notching out of the joist to get the roofline lower, but if you must, 50mm at most, and I would nail a bit of something along the wall underneath just to be on the safe side. As I said above, if you are planning on storing lots of weight up there, then consider hangers and a binder.

OK, on re-reading I see I have misunderstood. You are talking about taking the top corner of the joists off to fit them below the top line of the rafters. Well, with a birdsmouth and rafter feet overhanging, there will be a minimum thickness left in your rafter, so it won't be as per Bob's drawing. There is no problem cutting a good chunk off the top corner of the joist. It's standard practise.

[9fingers]

.....From the point of view of the roof alone, the rafters are in tension and so don't need to be very high. The rafter bear onto the wall plate. The problem comes from the storage requirement which put an imposed load on the the rafters. Could you contemplate any support pillars under your storage area? It would possibly give you another 100mm headroom all over.

Bob

Could you just explain this a bit Bob, please? Rafters are in compression in a simple truss, with the tie (bottom chord/ joist) being in tension. I can't see how anything stored on the joists imposes a load on the rafters.

If the joists are struggling with storage loads, then hangers are the traditional solution: a tensile member hanging down from the ridge board at every (say) 3rd rafter, bolted to a rafter and the joists, with a binder alongside on the top of the joists to ensure that they all act together rather than deflecting individually.

The explanation is that I made a mistake

is should have read

From the point of view of the roof alone, the JOISTS are in tension and so don't need to be very high. The rafter bear onto the wall plate. The problem comes from the storage requirement which put an imposed load on the the JOISTS. Could you contemplate any support pillars under your storage area? It would possibly give you another 100mm headroom all over.


Apologies

[Richard39]

I am so envious. My slab is about 30m from the nearest place I can get with a vehicle, every block, brick, slate and all the wood has been carried piece by piece up the garden.. That will save you a considerable amount of time!

It's not quite as straight forward as it appears. Out of view on the right is the access up the side of the house, which is quite tight. Any deliveries will have to be dropped there, and then hand balled to the slab. It's not 30 metres though, so its not too bad.

[Richard39]

Hi Richard, and welcome.

Your joists need to be 220 x 45/50 at 400 centres for that span, if they are to take a load (storage above). I suggest leaving an access door in the gable so that you can feed long lengths of stuff in. You shouldn't really be notching out of the joist to get the roofline lower, but if you must, 50mm at most, and I would nail a bit of something along the wall underneath just to be on the safe side. As I said above, if you are planning on storing lots of weight up there, then consider hangers and a binder.

OK, on re-reading I see I have misunderstood. You are talking about taking the top corner of the joists off to fit them below the top line of the rafters. Well, with a birdsmouth and rafter feet overhanging, there will be a minimum thickness left in your rafter, so it won't be as per Bob's drawing. There is no problem cutting a good chunk off the top corner of the joist. It's standard practise.

If my trigonometry is up to scratch, if I was to cut the corner as per Bob's excellent sketch above, I'd be cutting the joist at about a 37°angle from the outside edge of the wall plate, which is only 100mm wide (well, a bit less for CLS). Would that affect the ability of the joist to pass the weight of itself and its loading down through the wall? My gut feel is that too much of the joist would be removed at that critical point. The obvious plan of action would be to remove less of the joist, drop the wall plate height, and job done. The fly in the ointment is that I can envisage the internal height to the underside of the joists getting to about 2m, which starts to feel more like a shed . Out of interest, if I didn't intend to use the space for storage at all, what size joists would be recommended for this span?

Regarding the hangers and binders, presumably would this transfer some load to the rafters? Would the rafters need uprating to account for this?

Thanks for the help.

[9fingers]

I'm a bit tied up at the moment Richard but I'll try and do a Mk2 sketch. My feeling, yet to be proven, is that maybe a small chamfered section of ceiling at each wall will still give you a decent ceiling height over most of the area and the greater height joists.
I'll leave it to Mike to suggest the non storage joist height.
From memory of long time ago, 225mm x 50 over 4.2m would support a full blown residential floor which in turn from even rustier memory worked out to about 2 people per sq metre.

Bob

[9fingers]

OK here is sketch 2 to illustrate the idea



The lower end of the rafter is bolted to the joist and acts as a foot for the joist to give you a decent ceiling height and a low eaves height. It will need checking out for load bearing strength but hopefully illustrates a way you can get nearer to your targets.

Bob