Building a shed using Prefabricated House Panels

[JakCal]

Hi Fella's,

I'm a complete building noob and looking for advice.

I have some pre-fabricated panels, the type used in constructing houses/flats. They're various widths, but all are 2400mm tall and are constructed using 140mm x 40mm timbers, which are very heavy. I would like to use these to build a shed/workshop measuring approx. 5m x 3m beside my house. The intended site was rotovated quite extensively about 2 years ago and so I'm unsure how soft the ground still is.

Due to the weight of these panels I was looking for advice on what type of base I should be putting down. I need to keep the costs down as much as possible, but am looking for something that will stand the test on time. I've been thinking about a concrete base, railway sleepers, concrete pillars, perimeter footings, concrete bricks (there may be a method I haven't yet thought of yet).

I also have a quantity of old decking that I could use for the floor if need be, although I was originally going to use these to run off the side of the shed to the rear of the house.

Any thoughts / suggestions on this?

Thanks in advance

View media item 24949

 

[Deluks]

Sips panels? These would make for a very posh shed. Would be worth putting decent foundation, damp proofing and decent roof on these.

150mm concrete slab with A142 mesh rebar would be a straightforward starting point. If you can shutter so that it sits higher than the ground around it then you'll help to keep moisture out.

Or go the full monty with a proper concrete strip footing as if you were building an extension, and trench blocks/engi bricks upwards and sit the panels onto these. Hire skip, get digging!

Don't reckon on decking the inside unless it's the smooth variety, the grooves on decking are for non-slip purposes in the wet.

Once panels are fixed together (you'll likely need an internal column to support the long walls) you cover with breather membrane, batten and clad with timber.

 

[JakCal]

Hi Deluks,

thanks for the reply. As I said I'm a noob and a lot of the stuff you mention I've had to google as I don't understand. So if my questions seem stupid please bare with me.

Sips panels? These would make for a very posh shed. Would be worth putting decent foundation, damp proofing and decent roof on these.

Sips panels, not sure tbh. They're constructed using 150mm x 40mm, then clad with osb and some sort of plastic sheet. They're originally from Sydenhams and look like these - View media item 24954

150mm concrete slab with A142 mesh rebar would be a straightforward starting point. If you can shutter so that it sits higher than the ground around it then you'll help to keep moisture out.

Is the 150mm in addition to hardcore? I understand what you mean on the shuttering.

Or go the full monty with a proper concrete strip footing as if you were building an extension, and trench blocks/engi bricks upwards and sit the panels onto these. Hire skip, get digging!

Are you suggesting possibly combining both? Is the concrete strip footing the same as perimeter footings I've read about? Any ideas on costs, I went onto 1 calc and it suggested about 10 tonne of materials, but maybe I had my initial figures wrong.

Once panels are fixed together (you'll likely need an internal column to support the long walls) you cover with breather membrane, batten and clad with timber.

Confused on what you mean by internal column. Breather membrane (had to look up what you meant). I'm unsure but It has something like this already (I think).

My apologies once again for coming across a bit thick, I'm the sort of person that pictures / diagrams mean a thousand words and all that.

 

[Deluks]

Structural Insulated Panels, if they contain insulation then they probably are.

http://www.siphouse.co.uk/Houses.htm

did you get these from ebay by any chance?


Yes, you'll need min. 100mm hardcore beneath any concrete floor.

My suggestion of 150mm was to make it easy for you, you could also have a 100mm floor slab thats a bit thicker at the edges to take the walls, slightly more detail involved though.

If you go for a filled trench foundation, you can do a basic 100 mm slab for the floor (and pour it seperately)

Breather membrane is a strong fibrous synthetic material with tiny holes in.

By columns, I mean the longest walls (5m) are probably too long to stand unsupported, so you'll either have to build an internal partition wall, or put a column of steel or timber fixed into the ground to 'hold them up' midway.

You say these are heavy (to lift) but you will be building a relatively lightweight structure overall so a slab might be the best option. same as a garden shed but you'll be 'upping' the strength somewhat.

My thinking was that as these are used to build houses, then you may a well build a 'small house' and use it as a shed. Obviously no plumbing/gas but could still be converted to a granny flat or something in the future if you do a decent enough job on it now.

You should probably do some more googling, (and use the search function of this site) on foundations, concrete slabs and timber frame construction. and have a think about what type of roof you want (more googling)

 

[JakCal]

Hi again,


firstly, I wanted to quickly ask what you thought on the idea of using sleepers for the base? I rang a couple of places earlier on Monday and one yard had reclaimed Jarrah sleepers for £18.50 and new Oak for slightly more, this seems cost effective and sounds like a quicker option. But would they be suitable?

There are a number of reasons for looking at this option more than the concrete, but principally because our house is situated on a corner plot with no rear access point. We're approx. 200' from the communal carpark and even further from the road. Logistically, skips and several 1 tonne bags would be very difficult, but not impossible.

Structural Insulated Panels, if they contain insulation then they probably are.

http://www.siphouse.co.uk/Houses.htm[/QUOTE]

Thanks for the link, took a look. The panels I have differ in that they don't have any insulation. The osb is only clad to the exterior of the framework and the membrane attached to that. It's all circumstantial anyway as you certainly seem to know what I'm describing.

did you get these from ebay by any chance?

No, I bought them locally. I found a chap advertising sheets of ply for sale and I noticed he had these also.

Yes, you'll need min. 100mm hardcore beneath any concrete floor.

My suggestion of 150mm was to make it easy for you, you could also have a 100mm floor slab thats a bit thicker at the edges to take the walls, slightly more detail involved though.

If you go for a filled trench foundation, you can do a basic 100 mm slab for the floor (and pour it seperately)

Ok, I understand. What width and depth would you suggest for the trench?

Breather membrane is a strong fibrous synthetic material with tiny holes in.

By columns, I mean the longest walls (5m) are probably too long to stand unsupported, so you'll either have to build an internal partition wall, or put a column of steel or timber fixed into the ground to 'hold them up' midway.

You say these are heavy (to lift) but you will be building a relatively lightweight structure overall so a slab might be the best option. same as a garden shed but you'll be 'upping' the strength somewhat.

I understand

My thinking was that as these are used to build houses, then you may a well build a 'small house' and use it as a shed. Obviously no plumbing/gas but could still be converted to a granny flat or something in the future if you do a decent enough job on it now.

I've no intention now or in the future of making it a habitable building. It will only be used as a shed/workshop, but appreciate what your telling me.

You should probably do some more googling, (and use the search function of this site) on foundations, concrete slabs and timber frame construction. and have a think about what type of roof you want (more googling)

I thought about putting a double pitch roof with guttering. But I was thinking of having the roof trusses spanning the length rather than the width (I hope I'm explaing that ok). My reason for this is that I hope to build a decked veranda outside my backdoor. Where we could just walk along the decking and straight to the shed door. I thought it would make sense to slope the roof on the shed in the same direction as the veranda.
Something like this View media item 25006
Not that I'm anywhere near this stage, but your input on fitting the shed roof this way is very welcome.

Thanks for taking the time to respond.

 

[Deluks]

Well sleepers are heavy to lug about as well, shifting aggregates with a wheelbarrow isn't fun, but still doable.
You can hire powered 4 wheel dumpers that you walk behind.


You could also build your shed base and deck area all using a standard decking base of posts into the ground in concrete. If you can get the timber place to cut the oak sleepers for you into 6x6 lengths, these would last a lifetime, and might be a more economical use of the timber.

Your covered walkway would need a length of timber fixed to the house wall at the highest point (to support it's roof)
...if you extend this timber past the house by the proposed width of your shed, and stick a timber post on the end, this would support your shed roof at the apex, and the post can be the mid-span support for the longest wall of the shed.

Is your backdoor level with the ground outside?

 

[JakCal]

Well sleepers are heavy to lug about as well, shifting aggregates with a wheelbarrow isn't fun, but still doable.
You can hire powered 4 wheel dumpers that you walk behind.

Sorry to flit from one to the other as I'm still weighing up the options. I realise that concreting would probably be the best way, It maybe possible for a tipper to get up on the grass from the carpark and drop outside my house (unsure on what the neightbours would think), rather than the bulkbags dropped kerbside. This would remove the problem of the material sitting in the carpark and causing an obstruction while I shift it. I'll give a small local supplier a call tomorrow and see whether that's an option.

You could also build your shed base and deck area all using a standard decking base of posts into the ground in concrete. If you can get the timber place to cut the oak sleepers for you into 6x6 lengths, these would last a lifetime, and might be a more economical use of the timber.

I see what you mean. I've read various posts on deck bases using this method. Unfortunately, as the sleepers are from a reclaimation yard they don't have the facility to cut them.

Your covered walkway would need a length of timber fixed to the house wall at the highest point (to support it's roof)
...if you extend this timber past the house by the proposed width of your shed, and stick a timber post on the end, this would support your shed roof at the apex, and the post can be the mid-span support for the longest wall of the shed.

Totally agree with you. But I don't think I would be able to do without incurring planning fees of £300+ as when I had a recent visit from the local building control, they informed me that If I attached the shed to the house then I would need planning. Not sure, but if the support is attached to the house and then to the shed roof, I would assume they class this as the shed being attached to the house (pedantic I know). I was told that I could butt the shed upto the house though and so my intention was to have the both roofs right beside eachother.

Is your backdoor level with the ground outside?

No the height of the door from the ground is 8".

 

[Deluks]

Ok, if you want the deck area level with the back door, and the shed level with the 'verandeck', then you are going to have to raise the shed off the ground by about 8 inches then. So the concrete option will mean you having to ship in enough material to raise it all up.
Concrete footing>brickwork or single course of blocks> filled with 100mm hardcore and then 100mm concrete.

Most companies do 'kerbside delivery only' for 'insurance' (covering their ars if they break stuff) reasons.

8 inches is a decent height for a timber structure <meaning you will have a decent airflow beneath to unsure that is doesn't rot away in a few years.

You could use 4" standard fence posts set in concrete, soaking them overnight in some decent timber preservative for good measure.
Deck frame onto this incorporating the shed.

As for "when I had a recent visit from the local building control, they informed me that If I attached the shed to the house then I would need planning"

Building control and planning dept. are seperate entities. That advice should only be taken onboard if the planning dept. tell you so. Call them and see what they think.

Looking at http://www.planningportal.gov.uk/uploads/miniguides/outbuildings/outbuildings.html

As for 'shed not touching' then just build a 'goal post' using a couple of 4x4's and a couple of 8x2 nailed together to form the centre of the shed structure. (8x2's running along the apex.

 

[freddiemercurystwin]

Sorry to butt in here Deluks but for the record technically once it is attached to the house it becomes an extension in the eyes of the Planners. That's not to say it wouldn't come under Permitted Development though. It would also require Building Regs Approval, technically!

I'll butt out again now!

 

[JakCal]

Thanks for the contribution freddymercurystwin.

Ok, if you want the deck area level with the back door, and the shed level with the 'verandeck', then you are going to have to raise the shed off the ground by about 8 inches then. So the concrete option will mean you having to ship in enough material to raise it all up.

I'd like the deck area level with the back door. The shed doesn't have to be level just the entrance to the shed or if I have to I don't mind having a step if need be to the entrance to the shed or inside the shed.

Concrete footing>brickwork or single course of blocks> filled with 100mm hardcore and then 100mm concrete.

Most companies do 'kerbside delivery only' for 'insurance' (covering their ars if they break stuff) reasons.

Ok, Ive rang the local supplier I mentioned and explained what I was doing, he recommended 6" footing with a 4" base. He also said that he thought 2" of hardcore should be enough.

His quote:
3 Yards of Ballast + 15 bags of Cement @ £200.00
1.5 Yards of hardcore @ £55.00
All inclusive of vat & delivery.

He also said that he was happy to tip it directly outside. So that makes life a lot easier.

As for "when I had a recent visit from the local building control, they informed me that If I attached the shed to the house then I would need planning"

Building control and planning dept. are seperate entities. That advice should only be taken onboard if the planning dept. tell you so. Call them and see what they think.

Looking at http://www.planningportal.gov.uk/uploads/miniguides/outbuildings/outbuildings.html

I rang them and they did indeed confirm that if it was attached to the house then it would be classed as an extension, bummer.

As for 'shed not touching' then just build a 'goal post' using a couple of 4x4's and a couple of 8x2 nailed together to form the centre of the shed structure. (8x2's running along the apex.

That makes a lot of sense, I'll do a diagram later on to make sure I really do understand (you can see I like diagrams ).

It's now looking like I'll do the concrete base (sorry for all the faffing about ), what do you think of the building suppliers recommendations?

Thanks again, your knowledge has helped me immensely so far.

 

[Deluks]

Sorry to butt in here Deluks but for the record technically once it is attached to the house it becomes an extension in the eyes of the Planners. That's not to say it wouldn't come under Permitted Development though. It would also require Building Regs Approval, technically!

I'll butt out again now!

Feel free to butt back in again, I'm busy and have to rush out!
Sorry Jak, back later.

 

[Patho]

I am looking at doing something similar and looking at Embridges' site it would come under permitted development http://www.planningportal.gov.uk/england/public/buildingwork/projects/workcommonoutbuildings/

 

[JakCal]

I am looking at doing something similar and looking at Embridges' site it would come under permitted development http://www.planningportal.gov.uk/en...work/projects/workcommonoutbuildings/[/QUOTE]

Hi Patho,

Building Control & Planning explained that the principal was the same as a garage and quoted the following to me:

"Building a detached garage of less than 30 square metres floor area would not normally need building regulations approval if:

•the floor area of the detached garage is less than 15 square metres."

 

[freddiemercurystwin]

I am looking at doing something similar and looking at Embridges' site it would come under permitted development http://www.planningportal.gov.uk/en...work/projects/workcommonoutbuildings/[/QUOTE]

Hi Patho,

Building Control & Planning explained that the principal was the same as a garage and quoted the following to me:

"Building a detached garage of less than 30 square metres floor area would not normally need building regulations approval if:

•the floor area of the detached garage is less than 15 square metres."

JakCal, in respect of Building Regulations, just to clarify, if you build a garage with a floor area less than 15m2 you can do what the hell you want (ie build it out of straw if you liked).

However if the floor area is between 15 and 30m2 and within 1m of the boundary it needs to be built from largely non-combustible materials ie brick or block.

Anything over 30m2 needs to meet Building Regs Approval.

 

[JakCal]

Hi Freddy,

I don't think their point was the floor area or whether it was 1m within the boundary, as placing it next to the house I avoid that latter issue. I think it was whether I attached it to the house or not. Originally I intended to use the house to form part of the back wall of the shed, thereby saving me 8' of panel. But Building Control then pointed out that if I attached the shed in anyway to the house it would be classed as an extension. I contacted planning yesterday and explained about the "roof beam" for the roof being attached and they insisted exactly the reg would apply.

Here 's my original intention: View media item 25102
TBH, I don't want anyone to waste their time on this issue as I don't mind not attaching the shed or "the roof beam" to the house as long as you think it's not gonna fall down. My main concern is doing the foundation.

What do you think about the suppliers recommendations I posted earlier?