Workshop build - rafter end design

[mickthetree]

Well it seems this is the place to put a workshop build and as I am in the very early stages of mine I shall begin. Some of this is as much to get it clear in my head what I am doing!

Area
The plan is to clear an area at the back of our garden which is currently a jungle and locate my new workshop there.

The area is 9m wide. I would ideally like to put it 1m from each boundary giving me a 7m long workshop by 4m deep.

I have costed out a number of options and looked at some off the shelf workshop/sheds. These are normally built using 2x2 battens spaced 1m+ apart and do not seem to provide a huge amount on strength or security.

Walls
2x3s at 600mm centres from a reclamation yard.
Insulation between (again from the reclamation yard albeit new)
Breather membrane on the outside, OSB on the inside.
Spacer battens on the outside then covered with feather edge. Seems like the cheapest way to cover it and fairly attractive too.

I also need to factor in some windows and doors! My uncle fits UPC windows for a living and always has some old units coming out so hopefully that wont be an issue.

Floor
2x3 timbers at 600mm centers
1" Ply boards screwed on top.

Base
I cant afford a concrete slab. I think I have decided on that much.
Options - clear the area, dig out and fill with hardcore and sit large "bearers" on that, or indeed on concrete paving slabs. This should provide an air gap and plenty of drainage.
Or I could create a number of concrete posts for the bearers to rest on. My dads shed is some 30 years old and sits on brick pillars. It has lasted well, but then again there are no heavy machines in there.

Roof
3x2 battens at 600mm centers with OSB or ply boards covered with an EPDM.


Questions:
Any glaring mistakes I'm planning on making here?
will battens and boards be ok for the floor? Should I be including some sort of membrane in there too?
The insulation is 1.2" polystyrene sheets. Is this any good? I presume its better than nothing. With the OSB over the top would it provide much insulation? They do have kingspan sheets but these are 100mm thick and I can afford the thicker timbers.
Will a base resting on bearers be man enough to support my machines inside?

As you may have guessed my budget is tight and I'm trying to save money where I can, without compromising on structural strength or indeed creating something dangerous to be in!

We did discuss putting a much bigger budget into this and creating a much higher grade structure that would add real value to the property, but as we don't plan on selling it any time soon it didn't make financial sense.

Lastly, the workshop will be at the back of the garden, some 44 meters distance between it and the back of the house. I'm not entirely sure how this affects planning but I will be doing some more research this weekend.

Any comments greatly appreciated.

 

[Rob]

the only thing that leaps out at me is the floor. They use padstones (which is essentially your proposed method) in the US all the time with no problems but the bearing timbers resting on the padstones from which your floor will spring are much much more substantial than 3x2. Consider that you'll be putting heavy machinery on it as well and I think they need to be a lot more beefy. I was thinking more like 8x2 but some more experienced views will doubtless be along soon.

 

[mickthetree]

Hi Rob

Thanks very much for taking the time and I'm sure you are right.

I can get some heavy section timbers to rest on these and then sit the rest of the floor on those. That sounds like a very sensible suggestion.

I guess the issue then is it will raise the floor height up considerably. Not the end of the world in this instance as long as I can keep the overall height down.

I suspect that due to the distance from the house it may need to remain below 2.5m in total height,

Many thanks

 

[StevieB]

8x2 would be overkill I think - how many machines do you have that weigh over 100kg and would you ever move them (probably not in a workshop that size). You could increase the number of bearers in machine locations, but that does mean working out where you will want stuff before you build (or lifting the floor and adding them afterwards).

Easiest way to get solid padstones is to get some of the large corrugated drainage pipe, bury 2 ft into the ground and fill it with concrete - voila, ready made concrete piling for bearers to sit on. Much more stable than a paving slab.

Someone will mention timber and floors soon, so think about a concrete strip foundation and 2 layers of bricks to keep the sole plate off the floor - will extend the life of the building massively.

Other immediate thought from me - 44m of armoured cable will not be cheap, think about how you are going to get power (and water?) to your workshop.

Steve

 

[Mike G]

3x2 timbers to span 4M !!!! :eusa-naughty: :shock: :eusa-doh:

No no. Those need to be 8x2. Even if you used 6x2 you will end up with sagging, and should never, ever climb onto the roof (which is going to make maintenance an issue). Your other option is a socking great purlin through the middle, lengthways, and have some 4x2s spanning onto that, but that purlin will be a monster.

 

[AndyP]

Make you get started in the spring so you can be in the warm by autumn.

I get shivers just looking at Mike and Terry's winter builds.

 

[Rob]

Hi Rob

Thanks very much for taking the time and I'm sure you are right.

I can get some heavy section timbers to rest on these and then sit the rest of the floor on those. That sounds like a very sensible suggestion.

I guess the issue then is it will raise the floor height up considerably. Not the end of the world in this instance as long as I can keep the overall height down.

I suspect that due to the distance from the house it may need to remain below 2.5m in total height,

Many thanks

yup its a series of compromises really that are ultimately driven by a combination of the planning limitations and structural stability. I guess (though a lot of elbow grease) you could dig down, make sure the site drains very well by taking suitable precautions and then put the wooden floor bearers so top is around ground level. Obviously, you really want to avoid any puddling down there though so free draining is critical. One alternative....mixing a slab yourself (rather than readymix) is a hell of a lot cheaper and might be one way to skin the cat. Many moons ago I built my first shed. We dug and poured the footings over one bank holiday easter weekend. It was dam hard work for 4 of us but we got it done and saved a fortune on ready mix. We hired the mixer and it was just the material cost. Back then we used no rebar and the hardcore was salvaged from other building works. Because the labour was free (mates) it made a massive budget difference. In fact, I'd be prepared to bet it might even have been cheaper than the cost of doing with tantalised 8x2's because the material cost was for sand and cement only. Now I know with modern slab construction methods...you're meant to use 56 tonnes of cast iron!! But there's an awful lot of slabs out there that don't have any metal in and they're still working...still uncracked. Lest we forget....its a shed for goodness sake. Of course if it needs building control you'd have no choice but it sounds like you're going for permitted development from your post. Just a thought. Sometimes I think we go a bit belt n braces in this day n age!

 

[Mike G]

Good post, Rob......

But just to clear one little thing up: you can be building something under Permitted Developments rights, but still require Building Regs approval. Permitted Development rights are a Planning issue, not a Building Control issue.

 

[Halo Jones]

Planning seems to be different everywhere but if you are staying 1m from your boundary should you not be able to have a pitched roof 2 - 2.5m at eaves and 4.5m at the ridge?

In my experience it doesn't matter how far your outbuilding is from your house as long as it is not nearer a road than your house (which is what I fell foul of and required planning permission for my much smaller 'shop )

H.

 

[mickthetree]

Thanks for all the input guys.

I should clarify the roof as it was very brief. I plan on having a pitched roof made from trusses on the ground and raised into position. Some of the large sheds I have seen have much less wood in the roofs than this.

Like this

Do you think 3x2s would still be under engineered like this? I plan on having more of them and closer together.

I do have a mixer, but I had assumed that a base had to be poured in one continuous mix, not piecemeal over a day or two. It is a long way to cart all of the materials with barrows, but it can be done. I might be able to rope some of the lads in.

Failing that I could pour some trenches instead including a trench through the middle and sit the bearers across these, on top of a course of blocks with DPM. Can I pour trenches in sections rahter than one constant pour?

 

[Mike G]

Ah..a pitched roof. That's a whole other story. 3x2 is still too slim, but we can certainly sort something out with much smaller timbers than for a flat roof, which is what I assumed when I said 8x2s.

Trench-fill foundations can certainly be poured in sections. It's done all the time. You need a bit of ply with a couple of holes in it, and some short lengths of reinforcing bar sticking through those holes, to stop each pour against. Prise the ply away the following day, move it along to the next location, and start pouring again.

Remember the 3 critical design elements that go to making your build a workshop rather than a shed:

-a low brick plinth

-OSB on the INSIDE, not the outside of the frame

-batten out on the outside of your frame before fixing boards or rendering.

Insulation is cheap. Really cheap. Don't fall into the trap of spoiling this build for a ha'p'th of tar. Polystyrene is crap. It is dangerous crap, too, turning into nepalm if the building ever catches fire. You'd be better off with 3 inches of mineral wool (although that might be hard to source).

 

[mickthetree]

thats excellent Mike. Thanks for the feedback.

They do have some kingspan. I'll get them to check what thicknesses they have. It was all leftover from a massive building job and was going to be scrapped. Its amazing the timber they get. I'll take a few photos next time I'm up there. they had some huge gluelam sections up there today.

Can you point me in the right direction for calculating depth of foundation for the trenches? Thats a fantasic tip about the rebar!

 

[Mike G]

Foundation depth isn't something you can calculate. If this building isn't covered by Building Regs, and if you provide me with some photos of the site and tell me what the soil is, I can give you a guidance, but until you actually dig the trench, there is no way of knowing for sure.

 

[mickthetree]

thank you mike that is very kind of you. I'll break soil and let you know.

 

[Wizard9999]

Mick

Coming late to this, but if I understand correctly you are looking at 4m x 7m positioned 1m from the boundary with a pitched roof. Under 30m2 and at least 1m from boundary means no building regs. But within 2m of boundary means you will need planning consent for anything more than 2.5m high, which if you don't want to apply for consent probably gives you a problem with the planned pitched roof. This is a useful summary http://www.planningportal.gov.uk/permis ... buildings/

As Mike says planning consent and building regs are independent and triggered by different criteria.

All the best,
Terry.

 

[mickthetree]

Thanks Terry. I had read that guide and came to the same conclusion that 2.5 was going to be my maximum, so its good to hear someone else has read it the same. Looking at sheds on the market it seems possible to achieve the pitched roof within the height (just). I am only 5'8 myself so for me a reduced head height would not be an issue. If we were selling the property I would want to make it higher, but for me, I'm not so fussed.

A single pitch with larger timbers could be an option, but I do need some head height. My bandsaw is quite tall and I use my tenon jig on my table saw often.

I'll report back when I have got some more ground information.

 

[Wizard9999]

Mick

If you are staying below 2.5m I would seriously consider a single pitch 'flat' roof. Commercial sheds tend to achieve a pitch whilst keeping below 2.5m overall height by having very low eaves heights. The true benefit of a pitched roof is that in any circumstances eaves height is limited to 2.5m, so with a pitched roof you can have eaves at 2.0m plus and get a decent angle and still stay under the overall height limit of 4.0m. Without planning consent this will not be an option for you. So you will have to choose between low eaves or very shallow pitch. With the latter it will be little different from a 'flat' roof; with the former the overall volume of the workshop will be less than with a 'flat' roof.

One question though, is the area you are building on flat. It is not covered in the summary I linked to, but sloping ground has some advantages in terms of height, as my interpretation of the detailed guidance is that the 2.5m is determined from the highest point of existing ground level the shed is build on. So in the workshop I am building the highest point (back) is 0.3m above the lowest point (front) meaning the workshop can in effect be 2.8m above ground at the front. As it is sloping front to back this has been very helpful in allowing me to maximise height.

Terry.

 

[mickthetree]

Thanks Terry
The ground is actually very flat where we are so I dont think I could benefit from the sloping ground idea.
Something else that we have toyed with is the idea of having two structures.

A larger one with all of the machines then a smaller one with my workbench and hand tools which will be better insulated. They could even be connected in some manner. This may yield some further options.

 

[StevieB]

If you have 44m of garden to play with, could you not move it forward a meter? Also, what is around your boundary? If there are no neighbours to complain then 1m from the boundary may be less of a problem - especially as you say you are not looking to sell any time soon. Just a thought!

Steve

 

[Wizard9999]

Mick

Two structures could help avoiding building regs if you want more than 30m2, but will do nothing for height if they are both still less than two metres from the boundary. As Steve says though, this is the official position and circumstances may determine your attitude to the risk of non-compliance .

Terry.

 

[mickthetree]

thanks Steve

Interestingly the neighbours on one side have positioned a massive shed right up against our boundary, next to where I'm planning. This was a few years ago though. We get on very well with the neighbours on both sides, but not so much at the back. There was a land dispute there before we bought.

If we sited the shed against the boundary then the neighbours moved, any new neighbours could protest I guess. I believe there is some sort of time frame after which they cant, but I'd need to research that.

We plan on putting in an extension within the next two years, so we will be having visits from building control. I wouldn't want to have to move the shed once it is sited if they took umbridge at the proximity to the neighbours fence, even if the neighbours didn't mind.

Last night I stood at the back doors and looked into the abyss of the garden and wondered if I really want to be that far away from the house at night in winter. It seems the ideal place to locate it, but it means I'm not so close to the house if I am needed.

 

[9fingers]

Mick,

Over the years I have found that the building control officers are very willing to chat about proposals informally. If you have some sketches and maybe photos to show them you will possibly get a heads up.
They tend to have either a specific timeslot when a BCO will be in the office before they go off on site or you might have to make an appointment.
Sadly the planning people have been less accommodating in my experience and won't give off the cuff impressions.

Distance from the house need not be that much of a problem if you fit some sort of alarm back to the house.
See my BRUB topic.

Cheers

Bob

 

[Wizard9999]

Mick

From what you have said so far I do not think building regs are your problem, so the risk is a BCO comes to inspect your extension sees the shed and then checks if you have planning consent. Personally I would say the chances are slim, especially if it is 40m away and even more so if the <2m gap is from the back wall to the boundary and therefore not visible until close up.

There is currently a point where you can get confirmation no enforcement action can be taken, if I recall correctly it is ten years after the breach. This is called a certificate of lawful development. But the law could change between building and being eligible for one. There is no such period for building regulations as far as I am aware.

Terry.

 

[Rob]

don't forget the future risk of selling the house. If your shed (sorry....studio) drives a bus through the rules, a buyers surveyor will be bound to highlight it in the report and then you might put buyers off. I would stick to the rules.

 

[kirkpoore1]

3x2 timbers to span 4M !!!! :eusa-naughty: :shock: :eusa-doh:

No no. Those need to be 8x2. Even if you used 6x2 you will end up with sagging, and should never, ever climb onto the roof (which is going to make maintenance an issue). Your other option is a socking great purlin through the middle, lengthways, and have some 4x2s spanning onto that, but that purlin will be a monster.

Mick, what youre talking about is typically called a concrete pier foundation here. Mike is right, you need support down the middle. However, the good thing about this type of foundation is that if you need more support, put in more piers. One or even two rows down the middle should give you the support you need.

I may have some pictures from building the base of my storage shed a few years ago. I'll try to dig them up.

Kirk

 

[mickthetree]

Some time has passed since beginning this thread :lol: but that has given me time to reassess the construction methods and save up some more money.

I am now going for a classic "Mike" workshop on a proper concrete slab.

A window of opportunity has fallen this weekend which I am going to take advantage of. A friend is available with his digger to landscape the area and prep for the base.

I am coming in just over 2 metres from each boundary giving me a 5m wide x 6m long workshop. This will also allow me to go over the 2.5m height restriction so I can do a nice pitched roof.

I need to get bits ordered up for the weekend but wanted to clarify what I need:

Is type 1 hardcore the right thing?
http://www.wickes.co.uk/Wickes-Granular ... g/p/224665

I have a local builders merchant I use, but wickes seem pretty keen on price.

I plan on 150mm hardcore then 50mm sand then 100mm concrete base.

How do I allow for thickened edges of the slab? raise the inner area of the slab with thicker layer of sand?

Once the slab is poured do I trim off the dpm to the edge? I presume this would allow any water to flow off the slab. Or should it be raised above ground level? Back fill the edges with gravel?

I am also running water, electric, internet and burglar alarm through a conduit to be dug.

 

[Mike G]

........I plan on 150mm hardcore then 50mm sand then 100mm concrete base....

Is there a reason for so much hardcore? Normally, 100mm is plenty. I can only think you must be in some really awful ground (peat, for instance) if you think you need so much. You certainly don't need 50mm of sand. It really is just to protect the plastic DPM from sharp edges sticking out of the hardcore, so need only be a few mm thick. It settles into all of the voids, so you might be sensible to assume say 25 or 30mm thickness when calculating how much you need, but it really doesn't need to be thick over all the ground.

If you are going to thicken up the edges of the concrete, just dig a little more out, and whack the hardcore down with a tamper (the end of a sledge hammer will do) rather than using a whacker plate at those locations. I don't mind an oversite slab in a house being 100mm thick, but for a foundation/ raft like this, I would suggest 150mm, and if there are any trees in sight, or the ground is in any way dodgy (particularly clay), then put some reinforcing mesh 25 to 50mm up from the bottom of the concrete. If you really want to do 100mm of concrete, then your thickening around the edges should be substantial.

 

[mickthetree]

thanks for posting back Mike. I'm happy to reduce the hardcore! I was taking suggestions from another forum.

I've just found your workshop build thread and the relevant page on your slab. So a full load of concrete is 6 cubic yards which on a slab 5000x6000 would give a flat slab of 155mm. Do you think that would be ok? I certainly intend to include some mesh.

I do have trees nearby which have fairly recently been removed, but I'm guessing old roots will persist, or perhaps even die back. Nothing huge though.

 

[9fingers]

If as I suspect Mick that your dimensions have been chosen to fit in with PDR, the area in question is the internal floor area so you slab could easily be 200-400mm larger in each dimension.

I guess most concrete wagons are going to be metric these days so maybe 5 or 6 cu m in new money?

Bob

 

[mickthetree]

Thanks Bob, I am limited on the width at 5m to remain within 2m of side boundaries, but I could increase the length. Most of the materials I had costed up so far came in 3m lengths, although 3.6 seems quite common too so I could eek out a bit more length without impacting the cost too much. Although if a barrel load of concrete is 6cubic yards and needs to be 150mm thick that might limit me.

My current garage (which is coming down) is 7mx3m which is nice, but the added width is what I'm really after.

 

[9fingers]

Thanks Bob, I am limited on the width at 5m to remain within 2m of side boundaries, but I could increase the length. Most of the materials I had costed up so far came in 3m lengths, although 3.6 seems quite common too so I could eek out a bit more length without impacting the cost too much. Although if a barrel load of concrete is 6cubic yards and needs to be 150mm thick that might limit me.

My current garage (which is coming down) is 7mx3m which is nice, but the added width is what I'm really after.

Just a few things to consider and then decide to avoid the "if only" moments later on.

Good Luck
Bob

 

[mickthetree]

thanks bob
much appreciated.

 

[Mike G]

Personally, I would reduce the width to a max. of 4.8 metres, which is the longest readily available length of carcassing timber. You'll get longer, but there won't always be stock, there won't always be a good choice of straight pieces to select through. This will help with the roof and with the walls. Longer thinner buildings look better than shorter fatter squarish buildings, too.

 

[mickthetree]

thats a great tip Mike. I could afford to loose 20cm off the width. I could increase the length a tad to 6.6m which would give me 32 square meters (external).

 

[mickthetree]

Evening all
Things are moving on and my friend will be here this weekend to landscape the area and help construct the base.

In the mean time I have been revisiting the plans for the frame. A bit limited by my sketchup skills, but has help to iron out a few things and raise some other questions. more studs in the gables to add too!

I plan to sit the walls on a 2 brick high plinth as I have enough bricks left over from another job.

With the bricks, base plate, wall plate and studs I am wondering what height to make the eves. I could go to 2440 so I dont have to cut down the osb sheets, but that will result in a ridge height 3.9m. Playing with a tape I would be happy with an eves height (internal) 2100 which would give a ridge height of 3.4. Does anyone know what height they set their eves to?

Is there a known height to set the collar ties? I want to allow enough space to use the area above for storage, but have a nice head height too. Also I see you dont have them on all rafters Mike. I am going tor 600mm centers on my rafters and walls. Can I get away with leaving a few out to access the roof space?

I dont have a paslode so hammer and nails it is. Any recommendation on what gauge nails I should go for?

Many thanks

 

[RogerS]

One thought re a construction job like this is do what I did. I bought a Paslode, used it and saved a huge amount of time and energy and then flogged it on eBay. Think of it as long-term hire for £40 !

 

[Mike G]

.........With the bricks, base plate, wall plate and studs I am wondering what height to make the eves. I could go to 2440 so I dont have to cut down the osb sheets......Does anyone know what height they set their eves to?

Don't forget the height of the brick plinth. That would make an extremely imposing building in my view. Ugly, even. Mine is 2050 from top of slab to top of wall plate.

.......Is there a known height to set the collar ties? I want to allow enough space to use the area above for storage, but have a nice head height too. Also I see you dont have them on all rafters Mike. I am going tor 600mm centers on my rafters and walls. Can I get away with leaving a few out to access the roof space?

Traditionally, the max height of a raised tie is a third of the way up the rafter. I set mine at 2550 above the floor (to the underside). If I had my time over again, I'd lower that by 100mm. It's unnecessary head room, and it would make access somewhat easier as well as giving me a little more storage. It would also bring the lighting closer to work level.

 

[mickthetree]

that is great Mike, just what I wanted to hear. I had settled on 2.1m last night so that fits right in with what you are saying. And at 2.4m head height its going to be palatial! Cant wait.

Mike, if you dont mind, when putting down the DPM before the concrete pour is there a specific way to join the DPM? It is supplied in a 4m wide roll. Is there a certain type of tape to use?

Also when laying my ducting again that is going to pierce the DPM. Is there a proper method for doing this?

 

[Mike G]

There is a very specific tape for DPM. Any decent builders merchant will stock it. It is sticky and stretchy. The secret is to have a clean dry membrane to start with. If you have the luxury of space around the slab, you could double tape it by lapping the plastic 600 or 800mm, say, tape the join, then (carefully) turn the joined plastic over and tape from the other side. The same tape will do the repair around the cuts you make for any conduit (or drain pipes). Once you have everything in final position, you can cut a patch say 600 square with a better hole and slip it over the top of the conduit, then tape it in position, and to the pipe. Any cuts or manufacturer's holes in the DPM, again, a patch about 2 foot square, believe it or not, is what you need.

As a tip, think about where you will be pouring the concrete, and thus work out its direction of flow, then arrange your lap in the DPM such that the concrete will flow over the join from the top, holding the top sheet down rather than trying to push it up. Think of the concrete flowing downstairs rather than upstairs, albeit the stairs are only a few microns thick.

 

[mickthetree]

Great tips, thanks Mike

Roger, I hadn't seen your post before. I'll see what I can find. that is a great idea.

Thanks again!