New workshop build on pier foundations

UKworkshop.co.uk

Help Support UKworkshop.co.uk:

Baker1983

Member
Joined
25 May 2021
Messages
15
Reaction score
6
Location
Essex
Part 1

Having followed this forum for a while now and gained some really useful knowledge along the way, I thought it only fair to share my workshop build with others. I’ll be documenting the build as I go with photos and drawings, hopefully to help others and also to receive constructive feedback and maybe a little encouragement along the way.

The Plan

To construct a timber framed workshop measuring 5.4 x 4.2m at the rear of the garden as close to the boundary as possible. The back and sides will be clad in metal box profile sheets and the front face slatted timber (tbc). The roof will be a warm roof with an epdm covering. The workshop will be divided into a small storage area and the rest will be used as home office.

3.jpeg

View down the garden. A little bit over grown, but mostly all clear now.
1.jpg

Planning permission drawings.

Rewind to June 2021 - The Base



I would have liked to construct a concrete base, however with no access to the garden other than through the house, along with constraints with parking, etc. this just wasn’t an (easy) option, so instead I settled on a timber framed base sat on top of concrete piers. I watched a lot of tutorials on this technique which seems to be widely adopted in the US, but less so in the UK.

The thinking behind using this technique for the foundation;

1. Less concrete, so I could mix up small batches, just enough at a time to fill each pier.
2. All materials could be brought through the house in small quantities.
3. Whilst maybe not as good a concrete slab base, it would still be very stable and not succumb to rot / damp.
4. The piers could be raised out the ground slightly to provide air flow and keep the timber away from the floor.
5. I wouldn’t have to completely level the garden which slopes from its highest point (top right) down to the lowest point (bottom left) by about 40cm.

After clearing the garden and marking out the size using string lines, I then marked out where and how far apart my concrete piers would need to be. 16 piers in total, 4 across and 4 deep. The maximum span between two piers across being 1.8m.

I levelled out the area roughly and then using an auger I drilled down as far as I could in each of the 16 pier locations. Approximately 1m deep. I’d seen in the US that they use a kind of cardboard tube that’s then filled with concrete and this had been my intention, however after more thought I was concerned that the diameter of the holes which was restricted by the size of the auger wouldn’t be sufficiently wide enough.

In the end I dug out each of the holes to approximately 40cm square and using scaffold board as shuttering, constructed a square frame around each opening, ensuring the tops of each one were level with one another.

With the holes for the foundation piers dug and the scaffold boards level, I then laid out the framework on top, ensuring it was square and level and temporarily fixed the frame together with each timber sitting centrally over the holes.

With the frame in place, I then drilled through the timber frame in each of the pier locations ensuring the hole was centred on the dug hole below. Once all drilled, I dropped in a steel threaded rod through the drilled holes in the frame and into the hole below. Each rod was held in place with a couple of nuts from above.

Next I poured concrete into each hole creating the piers. Once dry, I removed the frame and now had 16 concrete piers, each with a steel threaded rod sticking out the top.

With the frame removed, I used polo-shaped rubber rings that are typically used under plant pots to raise them off the ground and placed these over the steel rods. These would sit between the concrete pier and the timber frame stopping any moisture or water sat on the piers from rising up into the timber.

Concrete Pier.jpg

Model of pier construction.
7.jpeg

Actual pier construction.

The frame then went back on and was secured in place with washers and nuts that sat just below the top of the timber. Any protruding steel rod was cut level with the timber using a grinder.

The frame was constructed with 4x2 C24 treated timber with the outer frame doubled up and bolted together. I should have probably used a bigger timber here to reduce flex, however as I wanted to keep the height low, I opted for doubling up the timbers and there doesn’t appear to be any flex across the spans.

Using mini joist hangers, I placed floor joists at 400 centres and then inlaid rigid foam insulation and foil taped the joints. These were sat on timber battens beneath the frame to stop it slipping out.

The next step, which I wasn’t sure about, but had seen someone else do it and seemed like a sensible idea, was to lay breather membrane over the top. This was laid with the outer face, facing downwards to hopefully reduce any moisture coming up through the frame. Not sure this was necessary as theoretically there shouldn’t be any moisture rising up, but thought it wouldn’t do any harm.

Over this I laid 22mm P5 tongue and groove chipboard, secured with screws and 5min wood glue.

6.jpeg

View of base prior to overlaying breather membrane and tongue and groove chipboard.
Change of plan

After I constructed the base, I re-thought about the overall design. I initially wanted to build the workshop under permitted development, however I really wanted a warm roof. Due to the size of timber I need for the roof span, plus the thickness of the insulation on top and the raised timber base, keeping within the permitted development height of 2.5m would create a very low internal ceiling.

As a result, I decided to apply for planning permission so that I could maintain a decent internal height and keep the warm roof. This is a fairly simple process and easy to do if you have some drafting / drawing experience. As I had built the base I applied for part-retrospective permission. Although an extra cost, for the extra head height I think it’s worth it.

Six weeks later I got confirmation that my planning permission had been granted. They didn’t even come out to visit, just asked for some photos to be sent to them.

Fast forward to March 2022

After being granted permission, I covered up the base with tarpaulin and didn’t touch it until nearly a year later and it’s from this point that I’ll be documenting the build on the forum.
5.jpeg

All wrapped up ready to begin again nearly a year later. PS. Tarpaulin isn't water proof!
 

Attachments

  • 5.jpeg
    5.jpeg
    267.1 KB · Views: 5

Lorenzl

Established Member
Joined
20 Feb 2022
Messages
139
Reaction score
82
Location
Cambourne
Is your project marked as garden room instead of workshop to get it through planning ;)

Looking good and neat; the piers are a good idea. I don't think the breather membrane was required as the foil insulation should keep out any moisture.

Out of interest where is your power feed? Having a sink?
 

Baker1983

Member
Joined
25 May 2021
Messages
15
Reaction score
6
Location
Essex
Is your project marked as garden room instead of workshop to get it through planning ;)

Looking good and neat; the piers are a good idea. I don't think the breather membrane was required as the foil insulation should keep out any moisture.

Out of interest where is your power feed? Having a sink?

I tend to use workshop / garden room depending on who I’m talking to. Do you think it would have made a difference to the planning permission calling it a workshop?
My plan for power is to run up through the side wall. I didn’t show this level of detail on the plans, but it’s something I do need to think about before going much further.
No running services such as a sink, although I did consider it, but felt it wasn’t necessary. Time will tell.
 

Sheptonphil

Scrumpy junkie
Joined
29 Dec 2012
Messages
1,241
Reaction score
415
Location
Somerset
Couple of points

When putting in for my workshop planning permission I was advised by planning officer to call it a hobby room. Somehow it evokes less concerns from neighbours, so ‘hobby room’ was applied for and granted with no comments from neighbours.
The membrane you’re about to lay on the floor before the P5, I would use DPM plastic sheet, not permeable membrane. There will be damp passing through the timber, so DPM will stop any ingress up through floor.

I used the same pier method building my 7m x 4m summerhouse, but with 250mm cardboard tubes. It’s absolutely not going anywhere, and ground levels are 300mm sloped. Saved a terrific amount of excavation.

looking forward to following progress, but do ask for ideas before doing things the hard way if you’ve no experience of this type of build. There is a vast amount of friendly, non judgemental advice available on this site.
 

Lorenzl

Established Member
Joined
20 Feb 2022
Messages
139
Reaction score
82
Location
Cambourne
Somehow it evokes less concerns from neighbours, so ‘hobby room’ was applied for and granted with no comments from neighbours.
Workshop potentially means noise whereas sunroom sounds peaceful

A friend of mine dropped himself in it as he descried the big workshop he wanted to build as a cow shed. He then got embroiled in farming regulations :rolleyes:
 

Baker1983

Member
Joined
25 May 2021
Messages
15
Reaction score
6
Location
Essex
Couple of points

When putting in for my workshop planning permission I was advised by planning officer to call it a hobby room. Somehow it evokes less concerns from neighbours, so ‘hobby room’ was applied for and granted with no comments from neighbours.
The membrane you’re about to lay on the floor before the P5, I would use DPM plastic sheet, not permeable membrane. There will be damp passing through the timber, so DPM will stop any ingress up through floor.

I used the same pier method building my 7m x 4m summerhouse, but with 250mm cardboard tubes. It’s absolutely not going anywhere, and ground levels are 300mm sloped. Saved a terrific amount of excavation.

looking forward to following progress, but do ask for ideas before doing things the hard way if you’ve no experience of this type of build. There is a vast amount of friendly, non judgemental advice available on this site.
Thanks. That’s interesting regarding the planning permission and what you call the space.

With the floor. I’ve already laid the chipboard over the frame and think it’ll be a hard job getting it back up again. I have rigid insulation between the joists and all the joiners and tops of the timber are covered over with foil / aluminium tape. Do you think that will be ok? I could also lay a DPM over the chipboard before the final floor finish goes down - but assume this would cause problems with the chipboard sweating as it would essentially be sandwiched between the insulation and DPM.

That’s good to hear someone else has used the pier method. Yes I think I worried too much about the diameter of the holes and as a result spent far to much time excavating.

Thanks for the advice. I think I’ll document what I plan to do first on here, then wait for feedback before I carry out the work and then show the actual construction.
 

Baker1983

Member
Joined
25 May 2021
Messages
15
Reaction score
6
Location
Essex
Workshop potentially means noise whereas sunroom sounds peaceful

A friend of mine dropped himself in it as he descried the big workshop he wanted to build as a cow shed. He then got embroiled in farming regulations :rolleyes:
I hadn’t really given it much thought about the naming of the space, so guess I got lucky calling it a garden room. To be honest though, it probably will be used as a garden room the majority of the time and if I do use it for any wood working projects, the neighbours will probably be happy that I’m indoors rather than on the garden making noise!
 

Cooper

Established Member
Joined
27 Jul 2016
Messages
295
Reaction score
298
Location
Bromley Kent
I used the same pier method building my 7m x 4m summerhouse, but with 250mm cardboard tubes.
A picture would be interesting. Does your roof have a large overhang to keep walls more or less dry?

Woops, I thought you meant to construct the garden room from cardboard tubes but on reading the dimension I presume it was to cast the piers.
Foolish me.
Cheers
Martin
 

Pedronicus

Established Member
Joined
4 Jan 2022
Messages
156
Reaction score
628
Location
Surrey UK
I hadn’t really given it much thought about the naming of the space, so guess I got lucky calling it a garden room. To be honest though, it probably will be used as a garden room the majority of the time and if I do use it for any wood working projects, the neighbours will probably be happy that I’m indoors rather than on the garden making noise!
The current neighbours may be OK with that assumption but all it needs is one (new) stroppy one to raise a complaint of noise and possible commercial use for a large can of worms to be opened.
 

Sheptonphil

Scrumpy junkie
Joined
29 Dec 2012
Messages
1,241
Reaction score
415
Location
Somerset
A picture would be interesting. Does your roof have a large overhang to keep walls more or less dry?

Woops, I thought you meant to construct the garden room from cardboard tubes but on reading the dimension I presume it was to cast the piers.
Foolish me.
Cheers
Martin
Yes, just the foundation piers.
3B415DE8-DF00-4B0E-9F41-A466CF4EAC77.jpeg
1178FC9E-EB40-437F-A0CF-6D7A0D42CEF9.jpeg
5F215E2D-CC6D-4AF9-AC40-A0EA2A84B698.jpeg
645DA65D-5FC7-4B0A-8E04-5D27A6E2394E.jpeg
 
Last edited:

Molynoox

Established Member
Joined
17 Jan 2021
Messages
366
Reaction score
207
Location
Billericay
Interesting thread 👍
What is the wall build up? You are over 15m2 so it gets interesting with the fire regs. stuff.
Martin
 

Baker1983

Member
Joined
25 May 2021
Messages
15
Reaction score
6
Location
Essex
Interesting thread 👍
What is the wall build up? You are over 15m2 so it gets interesting with the fire regs. stuff.
Martin
Hi Martin. Yes it does. I really liked what you did with your build and really enjoyed the process.

I know this particular topic gets discussed a lot. I think in part as there’s no real guidance in the building regs as to what constitutes ‘substantially non-combustible materials’. For example is it based on a volume, weight, surface area, etc? and this seems to change depending on the local authority. Some seem to include the overall structure including base and roof, for others just concerned with the walls adjacent to the boundary.

Interestingly I can’t find anyone that has been taken to court over this issue, which I assume is because the regs are ambiguous, even interpreted differently by those who job it is to enforce.

On my the longest wall, the timber would equate to around 10% of the total surface area, so assuming I use a fire rated insulation and non combustible cladding such as box profile metal cladding, then technically it would be substantially made from non combustible materials, but again this is dependant on how you measure. Equally if I was to use metal cladding, normal insulation and line the internal faces with fire rated plasterboard, then based on surface area the non combustible materials would equate to around 66%. This would clearly be different if based on volume.
 

Molynoox

Established Member
Joined
17 Jan 2021
Messages
366
Reaction score
207
Location
Billericay
Hi Martin. Yes it does. I really liked what you did with your build and really enjoyed the process.

I know this particular topic gets discussed a lot. I think in part as there’s no real guidance in the building regs as to what constitutes ‘substantially non-combustible materials’. For example is it based on a volume, weight, surface area, etc? and this seems to change depending on the local authority. Some seem to include the overall structure including base and roof, for others just concerned with the walls adjacent to the boundary.

Interestingly I can’t find anyone that has been taken to court over this issue, which I assume is because the regs are ambiguous, even interpreted differently by those who job it is to enforce.

On my the longest wall, the timber would equate to around 10% of the total surface area, so assuming I use a fire rated insulation and non combustible cladding such as box profile metal cladding, then technically it would be substantially made from non combustible materials, but again this is dependant on how you measure. Equally if I was to use metal cladding, normal insulation and line the internal faces with fire rated plasterboard, then based on surface area the non combustible materials would equate to around 66%. This would clearly be different if based on volume.
haha, I didn't realise you had spotted my mammoth build thread :D

everything you say about the interpretation of the regs. sounds theoretically sensible, however, like you already allude to, it doesn't really matter what the regs. say because it's up to the local planning officers to decide what is ok and not ok (as frustrating as that may be). For that reason I didn't really waste too much time getting into the definitions once I had realised that, and instead just setup a call with them to discuss my particular build.

they were very friendly, and actually gave me confidence in my build as they said it was a refreshing change from most of the stuff they see which isn't normally designed in a way that reflects any knowledge of the regulations. So I think you are already in a good position, having at least read through the regulations.
Its a bit like when you go abroad on holiday - if you at least make an attempt at speaking their language the locals are super friendly and usually help you out, even if its just a few words that you know

I think the regs are clear that you don't need to worry about the walls not on the boundary by the way, so I wouldn't expect any interpretation problems with that aspect.

In summary, I would recommend doing some sketches / CAD models showing your wall build up and setup a call with the local planning officers to explain it. Make sure you label all the materials precisely, even with brand names if that is relevant. I think if you go in with guns blazing like that they will be very open to your design ideas, rather than steer you down a 'standard' route

Martin
 

Yojevol

Clocking on
Joined
29 Jan 2017
Messages
931
Reaction score
391
Location
Cheltenham
When I put in for planning for my completely wooden w/s I was advised I needed to provide some fire rated material on the wall adjacent to the boundary. Why's that? I enquired. "To protect your neighbours property" was the reply. I pointed out that the neighbours property is an open field only ever used for horses, it doesn't even have a stable. The inspector said "Yes, it's a bit ridiculous in this situation. Just put up a layer of plasterboard on the inside to show willing and I'll pass it.
Brian
 

Baker1983

Member
Joined
25 May 2021
Messages
15
Reaction score
6
Location
Essex
When I put in for planning for my completely wooden w/s I was advised I needed to provide some fire rated material on the wall adjacent to the boundary. Why's that? I enquired. "To protect your neighbours property" was the reply. I pointed out that the neighbours property is an open field only ever used for horses, it doesn't even have a stable. The inspector said "Yes, it's a bit ridiculous in this situation. Just put up a layer of plasterboard on the inside to show willing and I'll pass it.
Brian
Hi Brian.
That’s crazy. This is the thing, there seems to be such a varied opinion. A friend of mine was told he would have to build using block work to meet the requirement, however I don’t think he put forward any other options for them to consider, so as Martin said above, I think it’s important to have a few options of how you think you can meet the requirement and then present these to the building officer and hope they agree.
 

Baker1983

Member
Joined
25 May 2021
Messages
15
Reaction score
6
Location
Essex
haha, I didn't realise you had spotted my mammoth build thread :D

everything you say about the interpretation of the regs. sounds theoretically sensible, however, like you already allude to, it doesn't really matter what the regs. say because it's up to the local planning officers to decide what is ok and not ok (as frustrating as that may be). For that reason I didn't really waste too much time getting into the definitions once I had realised that, and instead just setup a call with them to discuss my particular build.

they were very friendly, and actually gave me confidence in my build as they said it was a refreshing change from most of the stuff they see which isn't normally designed in a way that reflects any knowledge of the regulations. So I think you are already in a good position, having at least read through the regulations.
Its a bit like when you go abroad on holiday - if you at least make an attempt at speaking their language the locals are super friendly and usually help you out, even if its just a few words that you know

I think the regs are clear that you don't need to worry about the walls not on the boundary by the way, so I wouldn't expect any interpretation problems with that aspect.

In summary, I would recommend doing some sketches / CAD models showing your wall build up and setup a call with the local planning officers to explain it. Make sure you label all the materials precisely, even with brand names if that is relevant. I think if you go in with guns blazing like that they will be very open to your design ideas, rather than steer you down a 'standard' route

Martin
Thanks for the reply Martin. I did really enjoy the mega build / post! I could read posts like that all day long.
Thinking about this a bit more, I think you’re absolutely right. The Building Regulations set out the requirement. There are many ways to achieve that requirement and this gives the architect, designer, builder and homeowner some creativity as to how they achieve that requirement. If you ask them what their view would be, it would most likely be the simplest (belt and braces approach) way to achieve that requirement which would most likely be block work, etc. If however you present a creative approach / alternative method, then that provides them which something to consider in more detail.
Will be sketching up possible solutions and arranging a call with them to discuss.
 

Molynoox

Established Member
Joined
17 Jan 2021
Messages
366
Reaction score
207
Location
Billericay
Thanks for the reply Martin. I did really enjoy the mega build / post! I could read posts like that all day long.
Thinking about this a bit more, I think you’re absolutely right. The Building Regulations set out the requirement. There are many ways to achieve that requirement and this gives the architect, designer, builder and homeowner some creativity as to how they achieve that requirement. If you ask them what their view would be, it would most likely be the simplest (belt and braces approach) way to achieve that requirement which would most likely be block work, etc. If however you present a creative approach / alternative method, then that provides them which something to consider in more detail.
Will be sketching up possible solutions and arranging a call with them to discuss.
I think you have summarised that spot on there 👍
Martin
 

Baker1983

Member
Joined
25 May 2021
Messages
15
Reaction score
6
Location
Essex
Update

Hi Everyone. Have been giving more thought to the base I’ve constructed and after a quick calculation of the overall weight; base, walls, cladding, doors and roof, etc. I’m concerned my pier foundations with the timber frame sat on top may not be suitable.

I may be over thinking it, but perhaps a concrete base would be better. There is a significant amount of weight sat on the piers and I can’t help but think should one of those piers not hold up or sink slightly more than the surrounding piers, then the entire room will collapse.

Taking up what I’ve already done and replacing it with a concrete base is no easy task and obviously a waste of time and expense to date, however where my heads at, at the moment I don’t think I’ll feel comfortable unless I put in the concrete base. Starting again, would also allow me to provide more access around the perimeter and also the overall height would be lower (although I have planning permission for a higher roof level, I’m conscious it will sit high above the fence line and don’t want to upset any neighbours).

I guess without a structural engineer I’ll never know what’s best and I am a worrier about these things. Am I worrying over nothing?
 

Molynoox

Established Member
Joined
17 Jan 2021
Messages
366
Reaction score
207
Location
Billericay
I think if you are going to worry about something then the foundations are a worthy candidate, you could argue it's the most important part in terms of impact if it goes wrong.
I had a similar dilema to you actually, I was 95% sure that concrete piers would be strong enough, but by the time I had costed it all up, it wasn't much of a saving over groundscrews, and I fancied the idea of being 100% confident seeing as it was the foundations. I looked at a regular concrete base too and I think cost was similar ball park to groundscrews for a flat pad and more expensive for a gradient like mine (as the concrete pad gets big at one end thus needing more concrete). I also don't like the idea of wood sitting on top of a flat bed of concrete.

I think you are also wise to try and get the levels down at this stage - you can't make the building lower later :) I excavated down about 150mm at one end of mine and I'm really glad I did for same reasons as you.
Martin
 
Top