A Newbie planning a Garage/Workshop/Man Cave

[RTC]

There doesn't seem to be an Introductions section, so I will use this section to do so.
I'm not a 'real' woodworker I'm afraid. I'm an inveterate car tinkerer and more comfortable with a length of 40x40x3 RHS* steel and a MIG welder than 50x100 softwood and a plane. I’ve reached 59¾ (and I'm staying there) and benefit from early retirement so it’s finally time to rebuild that Jaguar that has been waiting for me.

Unfortunately my sons share my car tinkering interest and we now have 8 vehicles between the 4 of us – 3 of which are long term ‘projects’. The youngest vehicle in our family fleet is rapidly approaching its 10th birthday, my existing double garage has its own entity on Google Calendar and I never seem to be able to book a long enough ‘slot’ in it for my own project car!
So, having consulted SWMBO, completed her kitchen, utility room and 2 of the 3 bathroom refurbishments, I now have permission to plan another Garage/Workshop/Man-Cave exclusively for my own use (as if!). Getting permission to budget for it is a debate for another day!

I’ve been playing about with SketchUp and after many drafts over many months I have decided on the general arrangement of my Project.
I will post details of the general design – but it will not be another incredible Gambrel Roof trainee luxury retirement cottage with lots of beautiful and elegant detailing!
To date I have used SketchUp just to draw ‘chamfered boxes’ to give SWMBO a general impression of the various alternative styles, play with the limitations of Permitted Development, check shadow casting, vehicle accessibility etc. Now I’m getting down to actually designing the thing, I find my SketchUp skills leave much to be desired.

I’m almost cross-eyed from reading all the information I’ve downloaded from the Wibbly Wobbly Web. I’ve lost track of what I read where. I've worn out a calculator and my memory converting US Imperial Units to more comprehensible SI Units. Finally, to round of my exploration of a new subject I find plenty of conflicting information - what a surprise!
So I’m afraid I’ll be asking lots of questions that you may have seen before. I promise I will study the Build threads I have already read as a guest. I hope you will be as generous with your time and knowledge as I have seen others benefit from already.

Bob.

*Rectangular Hollow Section

 

[devonwoody]

Welcome to the wood nuts here. I am sure we will be delighted to see your progress and interest in our goings on.

I also returned to woodworking on my retirement and I find it a full time pastime so I wonder how it will fit in with that motor interest you mention.

 

[OLD]

I think the key to a great garage would be insulation (wall roof and base ) and a concrete slab design with insulation but also a strong floor just big enough so that rain is shed of the walls and not allowed to run under .You may like to use steel for roof support but its design would have to be engineered or copied from similar. timber designs are out there.
Do not forget to include for lifting heavy engines etc using plant or designing into the structure.

 

[RTC]

I think the key to a great garage would be insulation (wall roof and base ) and a concrete slab design with insulation but also a strong floor just big enough so that rain is shed of the walls and not allowed to run under .You may like to use steel for roof support but its design would have to be engineered or copied from similar. timber designs are out there.
Do not forget to include for lifting heavy engines etc using plant or designing into the structure.

Alas there will not be any woodwork as you chaps know it going on in there. I do such joinery and carpentry as required for household maintenance and upgrading , but that’s all.

The basic shape is 3750 x 8000 internal to framing to meet the 30m2 rule, eaves height 2470 to squeak under the 2500 rule, with a 35 degree roof pitch giving a ridge height of 3862 to squeak under the 4000 ridge height rule.

The Planning Portal shows that size does not need Planning Permission but does require Building Regulations approval. I will put together a portfolio of photographs, location maps, Google Earth images and detailed construction drawings and discuss it with both Planning and Building Regulations chaps before turning the first sod, just to be certain.

The interesting (read complicated!) bit is that I’m planning centrally placed full height cross dormers to give a central ‘cathedral’ ceiling. That’s the major part of the developing design that I am most uncertain about.

I want (need) an area with around 3000 clear height for lifting engines whilst the car is still on axle stands. I use a mobile engine crane, so there will not be any hoisting off the structure. Old Jaguar engines come out complete with gearbox at a 70 degree angle and weigh the best part of 500kgs! Land Rovers with external roll cage, parabolic springs and 'full-on' offroad tyres are very tall old beasts with some heavy components. I even have problems with more modern cars in my existing garage with 2400 ceiling height - the bonnet contacts the ceiling when the car is high up on axle stands.

Inevitably there will be some steel fabrications in the structure at some key points, but there will not be any need to design for non-standard loads. Workbenches and shelving will all be steel bearing directly on the concrete slab foundation.

The basic wall framing will be of Sawn Dry Graded Structural Softwood Treated 47.0 x 100mm C16 Strength Graded for structural use Pressure treated against decay, fungal and insect attack – that’s how my nearest timber merchant (Jewson’s) describes it. Wall stud spacing is planned on 600 centres. Roof framing will be on 400 centres – more (much more) of that later.
Generally I will follow the advice shown in the thread - build-a-shed-mike-s-way-t39389.html

An aside: I noted in the registered users on-line one chunkolini - the same one as on the MIG Welding Forum? – I’m rtcosic on there – the one with the obsession about electrolytic cleaning.

 

[RTC]

First question relates to understanding the terms used for grading timber.

I downloaded a copy of The Building Regulations 1991 Part A Structure 1992 Edition Fourth Impression with Amendments 1994 to use the 'span tables' in the appendix. This talks of SC3 and SC4. The builder's merchants’ catalogues talk of GS or SS and C16 and C24 and the timber being European Whitewood/Redwood. If I interpret Table 1 in this old edition of the Building Regulations then:

GS=C16=SC3

Is this correct?

This makes 3 posts so now I will read up about posting pictures/drawings etc

 

[devonwoody]

RTC. post three replies with just a full stop. :wink: :mrgreen:

 

[RTC]

RTC. post three replies with just a full stop. :wink: :mrgreen:

But it's a REAL question!

 

[RTC]

Testing how to upload SketchUp images. (looking for the crossed fingers smilie and failing)

Sort of works in my Preview, but I must remember it shows a 'screen shot' and not the full view.

SPAN of Floor and Ceiling Joists

I found the teaching materials for a joinery course at a technical college through an online search, although I did subsequently see reference to it in another thread (which I can't find again). I saved the pdf but not the source so can't now recall which college. This source defined span of joists as the EXTERNAL dimensions of the supporting wall - 3950mm in the sketch.

My rusty memory of doing simple beam calculations just over 4 decades ago says use the 'clear' span or INTERNAL dimensions - 3750mm - and this is how it is defined in my copy The Building Regulations 1991 Part A Structure 1992 Edition Fourth Impression with Amendments 1994, so that is how define SPAN in this application. It's not a vast difference but can be enough to push you to the next size up timber in the span tables.

SPAN of Common or Jack Rafters

The drawings in The Building Regulations aren't very clear as to exactly where span is measured, but by analogy with simple horizontal beams I would use 'clear span' - from intersection with wall plate to intersection with Ridge Board (or projected intersection of two rafters? 'Centre Line') measured along the centre line of the rafter. This is 2347.2mm in the sketch.

The technical college material defines the length (not span) of a rafter from the intersection with the outer edge of the supporting wall measured along a parallel line to the intersection with the ridge board - 2411mm in this case. Again not vast but annoyingly inconsistent.

Bird’s Mouth:

When I first started on this design I was seduced by some detailed drawings on a US or Canadian site that showed the Bird’s Mouth cut so that the horizontal face was the full width of the supporting wall. This didn’t leave much rafter left to support the overhang!
The technical college teaching materials used a D/3 and 2D/3 proportions where D = depth of the rafter. In the Buildings Regulations it just seems to require a minimum bearing length of 35mm and doesn’t state (or I haven’t found) an upper limit on how deep to cut – which seems odd.

I have used a ‘rounded’ version of the D/3 and 2D/3 ‘rule’ in the sketch - 30mm and 65mm which gives a bearing length of 52.3 mm which ‘looks right’ to me.

Am I on the right track here, or do I need to stop right away and start yet another new drawing?

 

[OLD]

Treated timber need only be used where it may come in contact with damp so bottom wall plate /door construction .
span is support point to support point .
Remember a triangle is a strong structure so the birds mouth does not need to be over deep.
Some American TV programs do code + 1 for timber sizes for a better than is required strength as you seem to be worried with the details this may be the way to go.Also modern manufactured trusses could be considered/costed.

 

[RTC]

Looks like all bets are off.
I've just learned that new 'Guidance Notes' on Permitted Development were issued in August or September. Previously I had been led to believe that if the eaves height at 1 metre from the boundary was at 2.5m then I could have the ridge line running parallel to the boundary at 4m. I couldn't have the 'gable' end within 1m of the boundary though, so a full cross gable was always going to be a 'stretch'. Also that the 1m was measured from the boundary to the external finish of the WALL, so roof overhang and rainwater goods were not considered (as long as they did not actually overhang the boundary of course!).
Now it seems that if ANY part of the structure is over 2.5m high then ALL of the structure (right down to rainwater goods) must be 2m from the boundary. That's useless to me as it would leave over 2m of 'dead ground' between the workshop and the boundary and bring the whole thing too close to the house for aesthetic comfort.

So how to make a 2.5m high flat topped box look vaguely acceptable. But previously it seems eaves height was taken as the height of the wall plate. The new guidance notes use the height of the external roof at a point vertically above the wall finish (inside or outside isn't clear to me). With a flat roof with joists 50x200 plus roof covering that would knock another 250mm or so off the usable headroom and render the building useless for my purposes.

So much for reducing bureaucracy to make life easier/cheaper for the householder. Unless of course you benefit from a 1 acre garden and you can plonk it down well away from any boundary.

 

[Dibs-h]

Why not just apply for PP. I live in a conservation area and applied for PP for my workshop (4m wide x7.5m long and 4m tall to the ridge) and attached garage (4m wide x 6m long and 4m to the ridge). Both buildings are next to the boundary wall. PP was granted the 1st time, albeit with a few conditions, i.e. reclaimed rosemary tiles and stone to the front of the garage - visible from the street.

Other than that - no real issues. Obviously all under Building Regs as well.

Done the workshop and slowly getting around to the garage.

Roof on both is 35 degrees. I bought a 2 post (single phase) carlift, which will fit nicely in the garage (getting to old to be kneeling down, tinkering with cars!

Dibs

 

[RTC]

Why not just apply for PP. I live in a conservation area and applied for PP for my workshop (4m wide x7.5m long and 4m tall to the ridge) and attached garage (4m wide x 6m long and 4m to the ridge). Both buildings are next to the boundary wall. PP was granted the 1st time, albeit with a few conditions, i.e. reclaimed rosemary tiles and stone to the front of the garage - visible from the street.

Other than that - no real issues. Obviously all under Building Regs as well.

Done the workshop and slowly getting around to the garage.

Roof on both is 35 degrees. I bought a 2 post (single phase) carlift, which will fit nicely in the garage (getting to old to be kneeling down, tinkering with cars!

Dibs

Yup. Plan B in the making (actually probably Plan Q by now!)

Just for 'discussion purposes' I spent the afternoon knocking up a maximum sized 'Box' that meets the Permitted Development rules - UGH!

Tried to attach the SketchUp Exported image but it's over 1MB and exceeds the 256kB limit. Presumably there is some cunning way of getting around that but it's beyond me at the moment.

I'll also enquire about prefabricated trusses and maybe a scissor truss would give me all the headroom I crave - at the expense of light duty storage above traditional ceiling joists:

A 2 post lift is on my long term wishlist too, (the creaking knees and weakening back are already present thank you very much) hence the paranoia about headroom. I had a full depth full length pit in my previous garage, but it was never as useful as I thought it would be. It was immensely hard work to dig it all out by hand too, but I was a few decades younger then.

 

[paultnl]

You can rent mini diggers quite cheaply and maybe "steal" 3 feet from the ground if you can run a ramp down in to the shed. Depends on your local water table.

 

[Dibs-h]

Yup. Plan B in the making (actually probably Plan Q by now!)

Just for 'discussion purposes' I spent the afternoon knocking up a maximum sized 'Box' that meets the Permitted Development rules - UGH!

Tried to attach the SketchUp Exported image but it's over 1MB and exceeds the 256kB limit. Presumably there is some cunning way of getting around that but it's beyond me at the moment.

I'll also enquire about prefabricated trusses and maybe a scissor truss would give me all the headroom I crave - at the expense of light duty storage above traditional ceiling joists:

A 2 post lift is on my long term wishlist too, (the creaking knees and weakening back are already present thank you very much) hence the paranoia about headroom. I had a full depth full length pit in my previous garage, but it was never as useful as I thought it would be. It was immensely hard work to dig it all out by hand too, but I was a few decades younger then.

I also need maximum headroom in my garage and after mulling over quite a few options - I'm virtually settled on a traditional rafter and purlin roof. At worst case the purlins might end up being Flitch beams, Glulam or just steel beams. Probably make the final call nearer the time.

I'd love something nice looking like the Kingposts I made for the workshop - but max headroom is essential, so that I don't have an "expensive" moment when the lift takes a car in the air! Probably have to spend a little time on CAD.

Dibs