Tiny Office/Shed Build

[Crumblybiscuit]

Hi Guys,

Got a small project of my own ongoing at the moment thought I would be able to add progress on here as well some questions. It's still at the starting stages.

Small garden, so the building needs to be fairly small too. I will be working from home more, and really need to separate work from home. I also need some storage for tools etc.

Project is within 2m of the boundary and in a small long weird shaped garden. So i needed to keep the total height under 2.5M. Dimensions are 4.5M x 1.6M (Did i mention I work in tech and was too ******** to keep sheet material sizes in mind when planning the size?). In my mind i opted for a pent roof as it looked easy for a novice like me, happy to be corrected on this as I could still change the plans.

Base

Prep - Previous owner had left the garden in a royal state. Cleaned and gutted it all, removed a tree trunk (tried all sorts, in the end I dug around it and went to town with a huge axe and got rid of it in a day).

I prepped the base using some huge, heavy and fat council paving slabs I had laying around! Absolute monsters these things were, nearly broke my back shifting them around. I dug down the rough size of the slabs. Compressed some hardcore added a layer of sand, layed some weed membrane all the way across and sat the slabs on top. The soil around my property is absolutely solid, getting or mixing cement would have been nice but for such a small shed I thought it overkill. Also i have to access my garden through my neighbours (terraced houses), bringing materials round is a royal pain.

Timber Base - I opted for a timber base from 4x2 pressure treated wood. Raised off the paving slabs to prevent it from rotting and sitting in water. Followed the standard guidelines on spacing etc and added noggins all over for my own sanity. Filled with insulating board and taped off to provide a seal.

I then boarded over this with 18mm OSB3, and mid pandemic work absolutely shot through the roof (70 hour weeks gave me no time, not complaining I know some people have been really badly impacted). The OSB3 will need replacing as it has been raining on it and my makeshift cover has been next to useless in protecting it....


Walls

I did more snooping around on forums and google (how i accidentally ended up here!). Decided that 3x2 should really help me reduce costs as i was originally going with 4x2. Everything is pressure treated . I also reduced the Wall OSB from 18mm to 11mm looking at advice. The timber merchant had some issues and delivered the right length and number but it is a higher grade than I paid for? C24 instead of C16.

My sister was having a huge house renovation and by chance i was able to grab two UPVC windows from her (will add the dimensions when i dig them out). Less than 12 months old, in perfect condition! I would like to add these into one of the walls to get some light into the shed.

Stud Spacing - 600mm

Wall Structure (More on this below from further reading) - OSB3 internal, insulation board, OSB3 external, breather membrane, featheredge.

Roof

3x2 Pressure treated timber again, this time at 450mm spacing as the roof is quite a small one. Will board over with 18mm OSB3, originally had planned for premium roofing felt but the more I read the more i change my mind! Pent Roof as it looked easy to install to a novice (make one wall taller and done, kind of). I was hoping with a bit of a slope I could add some guttering to avoid water collecting everywhere when it rains.

Questions/Amendments

Walls - I have done a lot of reading, MIke G's thread in particular has been very helpful:
1. I have changed the wall design to ensure the outermost layer (featheredge or whatever) has the recommended gap created by vertical battens before the membrane layer. In order to let air flow.
2. My previous wall structure from outside in was FeatherEdge>Space (battens)>Membrane>OSB3>Insulation (in between studs)>11mmOSB3. Am i right in assuming the outside OSB3 needs removing? I just felt like it would make everything a lot warmer, but it seems it may inhibit the breathability?
3. Insulation, primarily i want the shed to be warm hence the reason for selecting insulating board over wool. Wouldnt this create a seal and stop the building breathing?

Roof
1. By spending about £60 more, I can move from "premium" felt to EPDM. Seems like a no brainer to me. I was going to paint over the felt etc for belt and braces.
2. Anyone disagree with me thinking that the pent roof is easier for a novice to build? Considering my height restrictions etc.
3. Insulation, again thinking of going with insulation board. May have to go for something quite thin as I understand I need to leave an air gap?
4. Venting - I could cry, i have read so many forums with so many different opnions and still don't understand half of this. More reading for me to do to get an understanding of what it all means.

Random - For a shed this size, would you guys normall add guttering? I live in West Yorkshire for reference, just didn't want rain from the roof causing puddles sludge etc.

I need to collect pictures of the progress so far and post them.

Thanks in advance for any assistance!

 

[Jameshow]

My thoughts why 1.6m deep.

1.8m would be the minimum I'd build too.

I'd use a pent roof for ease of build.

If using upvc windows it's a no brainer to use a uPVC door. Greenframe in cleckheaton are good. About £100 depending on condition.

For timber I use henshaw timber in Baildon thier t+g cladding is cheapest anywhere and quality 20mm Swedish timber.

I'd put a vent in the roof perhaps a caravan dome vent?'

EPDM makes sense.

Yes put a length of guttering along the rear.

Cheers James

 

[Awac]

https://www.specialinterestmodelbooks.co.uk/product/workshop-construction-no-23/Jim Forrest & Peter Jennings

Workshop practice series books. This book on small workshop construction is packed with good ideas and can really help with things you might not have thought about, and only £7.95. Helped me.

 

[Crumblybiscuit]

My thoughts why 1.6m deep.

1.8m would be the minimum I'd build too.

I'd use a pent roof for ease of build.

If using upvc windows it's a no brainer to use a uPVC door. Greenframe in cleckheaton are good. About £100 depending on condition.

For timber I use henshaw timber in Baildon thier t+g cladding is cheapest anywhere and quality 20mm Swedish timber.

I'd put a vent in the roof perhaps a caravan dome vent?'

EPDM makes sense.

Yes put a length of guttering along the rear.

Cheers James

Thanks for taking the time to reply James.

Why 1.6? Inexperience is all lol. Plus a really tight garden.

Thanks for the recommendation for the door I am about 20 minutes away from them!

Noted on the vent. I need to brush up my understanding on them anyway. Will keep that in mind as well as the timber merchant you mentioned.

Looks like EPDM is going to be the way to go.

 

[Crumblybiscuit]

https://www.specialinterestmodelbooks.co.uk/product/workshop-construction-no-23/Jim Forrest & Peter Jennings

Workshop practice series books. This book on small workshop construction is packed with good ideas and can really help with things you might not have thought about, and only £7.95. Helped me.

Hi. Thanks for the recommendation. I will get one ordered!

 

[Awac]

https://finewoodworking.com/FWNPDFfree/011160044.pdf
I just posted this on a different post, but you might like it as well. Enjoy your build.

 

[Fitzroy]

You don’t need the OSB on the outside of the wall. EPDM for the roof yes it’s a no braini I’d think hard on if you want a roof penetration as that will complicate your EPDM, not too difficult but it introduces a leak point. I found the pent roof easy but permitted development limits your eave height. With a regular roof both eaves are the same height with a pent roof one is lower than the other, so reducing your minimum height inside.

You don’t need to vent the walls as the backside of the insulation is open, once you exclude OSB. Roof venting is IMHO contentious, ideally you vapour barrier on the warm side of the insulation and vent the cold side. If you only vapour barrier you run the risk of condensation on the underside of the roof board behind the EPDM if any moisture gets beyond the vapour barrier. I’d be thinking about how much time you will occupy (ie time generating moisture risk vs time drying out) and how long you want the building to last 5, 10, 25years. Lots of occupancy and a 25 yr building vent it, less occupancy and 10years don’t stress it.

max out the insulation within the framing, and watch for the details, foam around insulation gaps and tape joints. If you ignore the details you can easily screw up the spend you’ve committed to the insulation.
Fitz

 

[Awac]

The next roof I do I want to use metal sheets, here is an interesting fact sheet that might help. I was reading about how they metal sheet roofs in Australia, heat and cold nights is a recipe for condensation, you really do not want that. Metal sheets that sandwich insulation.

https://www.mcrma.co.uk/pdf/mcrma_t06.pdf

 

[Jameshow]

Agreed don't put anything through the roof of the EPDM.

Rather put some vents under the eves.

Cheers James

 

[Keefy.]

Overkill for what you need but take a look at some of Oakwood Garden Rooms video's on faceache, you can get good tips off there.

 

[Glitch]

Based on recent experience as a noob shed builder.

-Walls need to be right on the edge of the slabs to avoid splashback.
- Make sure everything is square - the studs, the individual frames, the corners and the rafters. Especially with 3 x 2 600mm centres
- OSB is usually imperial - 8' x 4' so I used imperial spacing, either 16" or 24" to help reduce board cutting.
-EPDM for the roof and a gutter on the lower side makes sense but think about where it's going to drain to. It's surprising how much water it catches.
-OSB on the inside only seems to be the safer option. I think that needs rockwool for breathability although I have used Thermafleece - real wool product and pleasant to handle. Shed smells like a farmyard barn though
- Think carefully about the door and window openings. Right sizes and the finished look. I didn't think about door lining and how to get door flush with cladding (and still trying to work it out)
-Painting long boards both sides in winter is going to be a challenge (assuming you're painting). Low temps, dew, frost and rain can play havoc with drying time and paint finish. Depends on your timelines but might be worth waiting for warmer spring days for the final cladding.
- at least 50mm gap between top of roof insulation and underside of roof OSB with unobstructed airflow between the rafters
- 3x2 sounds a bit lightweight for the rafters but it is only a 1.6m span with 450mm centres - More knowledgeable people can advise on that.

Good luck. It is satisfying constructing your own garden buildings!

 

[Awac]

Based on recent experience as a noob shed builder.

-Walls need to be right on the edge of the slabs to avoid splashback.
- Make sure everything is square - the studs, the individual frames, the corners and the rafters. Especially with 3 x 2 600mm centres
- OSB is usually imperial - 8' x 4' so I used imperial spacing, either 16" or 24" to help reduce board cutting.
-EPDM for the roof and a gutter on the lower side makes sense but think about where it's going to drain to. It's surprising how much water it catches.
-OSB on the inside only seems to be the safer option. I think that needs rockwool for breathability although I have used Thermafleece - real wool product and pleasant to handle. Shed smells like a farmyard barn though
- Think carefully about the door and window openings. Right sizes and the finished look. I didn't think about door lining and how to get door flush with cladding (and still trying to work it out)
-Painting long boards both sides in winter is going to be a challenge (assuming you're painting). Low temps, dew, frost and rain can play havoc with drying time and paint finish. Depends on your timelines but might be worth waiting for warmer spring days for the final cladding.
- at least 50mm gap between top of roof insulation and underside of roof OSB with unobstructed airflow between the rafters
- 3x2 sounds a bit lightweight for the rafters but it is only a 1.6m span with 450mm centres - More knowledgeable people can advise on that.

Good luck. It is satisfying constructing your own garden buildings!

Have a look at that link to “workshop construction” book I put in earlier. It‘s not a big book, but jammed with information and drawings for small workshop construction, and only £7.95. Has all span charts as well. I can’t praise it enough.

 

[Glitch]

Have a look at that link to “workshop construction” book I put in earlier. It‘s not a big book, but jammed with information and drawings for small workshop construction, and only £7.95. Has all span charts as well. I can’t praise it enough.

Book sounds really good but I'm too far into my build now - cladding stage. Mistakes have been baked in Nothing I can't live with though.
I'm finding all the great advice a little too late. Kicking myself for not finding all this info a few months ago!
Happy to share my own shed learnings if it helps others.

 

[jcassidy]

I'm getting the interior cladding on my small workshop. I too am limited by the available space, so it's long and narrow - 16 feet x 6 feet. It was going to be 12x6, but I noticed the full length boards gave a pleasing symmetry to the garden, and saved myself the hassle of cutting them.

All the cladding is recovered heat-treated shipping crates, typically 20mm thick. The quality of the wood from crates is so poor I would be reluctant to build any load-bearing structures with them, but they're great for cladding. As long as you bin/burn all the rot-infested ones. I have a fair pile now waiting to be brought to the local recycling facility.

Exterior cladding had a rough T&G cut into them, treated with anti-fungal stuff and then a couple coats of shed paint. Under the cladding I have a 25mm air gap, then 50mm polystyrene foam insulation (free from a demolition site), then vapour barrier, then interior cladding (again, recycled crates but planed flat on the interior face).

Flooring is 100mm Kingspan Xtratherm insulation between the joists, covered by vapour barrier and 18mm ply. The ply wasn't sufficiently solid so I covered that with, guess what? Planks from crates. I will leave a few weeks to dry sufficiently and then nail 'em down and sand 'em flat, possibly with a varnish finish. I was neglecting the fact that I want a perfectly horizontal surface, so I may have my work cut out there as I wasn't checking when I laid down the planks. The plywood was flat, but the boards are slightly different thicknesses!

Roof is felt, 18mm ply, 25mm air gap, Kingspan Xtratherm 25mm, vapour barrior and 9mm T&G planking. I felt the recovered crates would be too heavy and too ugly for overhead.

I ensured free air flow through of the walls and up around the roof space, venting to the outside obviously.

I installed a double-door for moving projects in and out, and a traditional shed door. Both will be insulated with Xtratherm, clad with thin veneer flooring I got from a neighbour (to reduce the weight), and both open outwards.

I have two small windows, simple plexiglass, but I've made sure to fill all the gaps around with expanding foam, ditto for the doors and any glaring gaps between insulation panels.

My flat-roof inclines inwards as I didn't want water running along the boundary behind the shed. I don't have any need for guttering because a) the eave is too low, b) the water is falling onto gravel, and c) I'm too cheap to buy guttering.

Anyone need about 2 kilos of crooked nails yanked out of crates?
Photos to follow.

 

[Crumblybiscuit]

You don’t need the OSB on the outside of the wall. EPDM for the roof yes it’s a no braini I’d think hard on if you want a roof penetration as that will complicate your EPDM, not too difficult but it introduces a leak point. I found the pent roof easy but permitted development limits your eave height. With a regular roof both eaves are the same height with a pent roof one is lower than the other, so reducing your minimum height inside.

You don’t need to vent the walls as the backside of the insulation is open, once you exclude OSB. Roof venting is IMHO contentious, ideally you vapour barrier on the warm side of the insulation and vent the cold side. If you only vapour barrier you run the risk of condensation on the underside of the roof board behind the EPDM if any moisture gets beyond the vapour barrier. I’d be thinking about how much time you will occupy (ie time generating moisture risk vs time drying out) and how long you want the building to last 5, 10, 25years. Lots of occupancy and a 25 yr building vent it, less occupancy and 10years don’t stress it.

max out the insulation within the framing, and watch for the details, foam around insulation gaps and tape joints. If you ignore the details you can easily screw up the spend you’ve committed to the insulation.
Fitz

Agreed on the OSB it looks like that is the way to go. Although it feels like it will be quite cold without it!

EPDM roof is going to the the option and I don't fancy cutting through it etc so will need to decide on the venting.

I will need to switch insulation going this way. Which is fine, luckily I haven't purchased any just yet.

I'd be chuffed if I can get 10 years out fo the building for my first time doing anything like this.

Appreciate your assistance.

 

[Crumblybiscuit]

Based on recent experience as a noob shed builder.

-Walls need to be right on the edge of the slabs to avoid splashback.
- Make sure everything is square - the studs, the individual frames, the corners and the rafters. Especially with 3 x 2 600mm centres
- OSB is usually imperial - 8' x 4' so I used imperial spacing, either 16" or 24" to help reduce board cutting.
-EPDM for the roof and a gutter on the lower side makes sense but think about where it's going to drain to. It's surprising how much water it catches.
-OSB on the inside only seems to be the safer option. I think that needs rockwool for breathability although I have used Thermafleece - real wool product and pleasant to handle. Shed smells like a farmyard barn though
- Think carefully about the door and window openings. Right sizes and the finished look. I didn't think about door lining and how to get door flush with cladding (and still trying to work it out)
-Painting long boards both sides in winter is going to be a challenge (assuming you're painting). Low temps, dew, frost and rain can play havoc with drying time and paint finish. Depends on your timelines but might be worth waiting for warmer spring days for the final cladding.
- at least 50mm gap between top of roof insulation and underside of roof OSB with unobstructed airflow between the rafters
- 3x2 sounds a bit lightweight for the rafters but it is only a 1.6m span with 450mm centres - More knowledgeable people can advise on that.

Good luck. It is satisfying constructing your own garden buildings!

Lots of points to consider there and think about.

Looks like I will take your and everyone else advice on OSB internally only and switching to Rockwool etc.

Thanks for taking the time to respond. I will update the post once I have done a little more research.

 

[Awac]

Preserve what you have built. I love this stuff.
When I build a shed for the wife I made the window frames and we carved them in an natural form sort of way, and then I decided to get arty and linseed oil them, sigh...the sun in France is fierce in summer and it did not last long, so I looked around for something else.
This is a great coating for wood in a shed build. Non-Toxic Wood Treatment that lasts a lifetime.A powder concentrate (£20) that will make up to one gallon of treatment. Just mix with water.
Apply to bare, untreated or pressure treated wood using normal application methods. An all-purpose treatment for all new wood without need for maintenance. There is no need to ever scrape, re-stain or worry about fading and wear.
Works by penetrating wood fibres to create a natural buffer against water and fungal decay. It increases wood's durability while creating an aged, silvery patina after just a few hours.

Canadian manufacturer (see video)
https://ecowoodtreatment.com/
UK importer
Eco-Wood Treatment - Harrod Horticultural (UK)

https://www.amazon.co.uk/Eco-Wood-Treatment-793573760104-Gallon/dp/B00KX05BE2

 

[Crumblybiscuit]

Hi All,

Sorry for the delayed update. Despite the freezing temperatures I have been slowly moving along with this build. I'm now at the stage where the timber structure is up, breathable membrane all round. Roof is on.

I haven't got lots of images of the progress as it has been me on my own trying to put this all together for the most part. Nearly fell flat on my backside trying to put the walls up until my wife assisted me.

 

[Crumblybiscuit]

It hasn't been feasible to get the EPDM roof up due to the temperatures. And i don't quite fancy trying to use contact adhesive on it all, which i assume is what I would have to do in colder temperatures instead of using water based adhesive. So what I did instead, to protect the roof. Was to buy some cheapo roofing felt and slap that on. To at least protect the roofing deck for a few months until more agreeable temperatures arrive. I got it all done in a few hours due to the small size and it barely cost me £40.

I did dabble with the idea of metal sheets for roofing, but the cost came close to EPDM and I have just decided to stick with EPDM for now.

I now have some further questions about various items to move the build on. I was hoping to get some insight on here.

1. Cladding - I was hoping to use metal sheets like this (32/1000 Box Profile 0.5 Thick Galvanised Roof Sheet) horizontally to clad the back of the shed facing the fence. It works out cheaper and faster than wood cladding and no one is going to see that side. Can anyone see any issues with this?

The rest of the shed I was hoping to clad with featheredge.

My local builders merchant quoted me for featheredge and they only have 125mm x 10mm featheredge. Usually used for fencing. Is that too thin for cladding? The alternative is Shiplap at 19mm. I am trying to keep the costs down if possible, but don't want to skimp either. I may need to look at a local timber place if the size is too thin.

I don't have the space to buy non treated wood and ensure it is treated before cladding the exterior. I was hoping to just purchase something already treated to save time.

2. Insulation - I changed my plans after reading Mike's post on building a shed. My question is around the RockWool vs PIR options. My shed would be more for a small office AND a little bit of DIY work. I can see that PIR provides better thermal protection when compared to Rockwool. Would i be causing myself any issues by doing so? Or do I need to just go ahead with rockwool?

I also figured out a solution to airflow in the roof. I am going to add some soffit vents at the front and back of the roof. This should allow air to pass through and out, ventillating the roof. Not something I had considered until I read the post from Mike and your replies. I may need to drill some small holes in the noggins to allow air to pass through however.


As usual any input at all is appreciated. It is my first build and I am sure i will have made mistakes. Although I couldn't believe my eyes when everything was level and the corners all measured up the same!

 

[Woody2Shoes]

Based on recent experience as a noob shed builder.

-Walls need to be right on the edge of the slabs to avoid splashback.
- Make sure everything is square - the studs, the individual frames, the corners and the rafters. Especially with 3 x 2 600mm centres
- OSB is usually imperial - 8' x 4' so I used imperial spacing, either 16" or 24" to help reduce board cutting.
-EPDM for the roof and a gutter on the lower side makes sense but think about where it's going to drain to. It's surprising how much water it catches.
-OSB on the inside only seems to be the safer option. I think that needs rockwool for breathability although I have used Thermafleece - real wool product and pleasant to handle. Shed smells like a farmyard barn though
- Think carefully about the door and window openings. Right sizes and the finished look. I didn't think about door lining and how to get door flush with cladding (and still trying to work it out)
-Painting long boards both sides in winter is going to be a challenge (assuming you're painting). Low temps, dew, frost and rain can play havoc with drying time and paint finish. Depends on your timelines but might be worth waiting for warmer spring days for the final cladding.
- at least 50mm gap between top of roof insulation and underside of roof OSB with unobstructed airflow between the rafters
- 3x2 sounds a bit lightweight for the rafters but it is only a 1.6m span with 450mm centres - More knowledgeable people can advise on that.

Good luck. It is satisfying constructing your own garden buildings!

In the UK, one of the major suppliers of OSB is Norbord, near Inverness, and their standard board sizes are metric (2400X1200 not 2440X1220) - but you're right to advise caution, because it is possible to create unneccesary waste/work for yourself.

One of the most useful features of guttering is to help keep the walls dry (from what would otherwise come down onto them from the eaves - rain is usually accompanied by wind!).

Cross ventilation at the eaves is a very good idea.