SIPS Garden Office for 3k?

[Ferdinand]

Inspired by this thread from @mrfish, Can we have a thought experiment as to just what it costs to build an insulated garden office with reasonable facilites? (Also because I still need something like this). I wamt to think through cost-effective options and see if I have not though about any aspects.

 

My £3k number is because more-or-less this is what it costs to buy a secondhand insulated, wired, site office of this size and spend £400 shipping it in.

 

My specification is for:

 

1 - 8 x 12 ft insulated garden room, capable of being practically used all year round.

2 - 2 x double electrical socket, water, lighting and drainage.

3 - Building base.

4 - I want to be able to dismantle it and rebuild (eg every few years). This is perhaps a personal requiremnt for me.

 

I am excluding items difficult to compare:

 

1 - Labour to build and fit out, because most of us could do this ourselves.

2 - Supply connections, as they could all be different depending on the circumstances.

 

Ferdinand

 

[Onoff]

Pre made SIPs or make your own? There's a few YouTube vids and bits on the GBF of people experimenting gluing unfoiled PIR / EPS to OSB. A bit I read about on GBF using "DM Easy" I read was interesting. From this place:

 

http://www.creffields.co.uk

 

[Ferdinand]

4 minutes ago, Onoff said:

Pre made SIPs or make your own? There's a few YouTube vids and bits on the GBF of people experimenting gluing unfoiled PIR / EPS to OSB. A bit I read about on GBF using "DM Easy" I read was interesting. From this place:

 

http://www.creffields.co.uk

 

 

I am wanting to explore ideas.

 

 

Edited May 31, 2017 by Ferdinand

[Crofter]

Here's my take.

Floor: Suspended 6x2 joists at 400ctrs (£100), filled with rockwool (£30); 9mm OSB underfloor layer (£20); chipboard on top (£50)= £200

Walls: 2x4 studs, 150m tot (£300), filled with rockwool (£65), with 9mm OSB sheathing outside (£70) and plasterboard inside (£50)= £485

Wall cladding: battens/ounterbattens (£30); corrugated steel= <£300

Ceiling/roof: 2x4 joists at 600 ctrs (£40) filled with rockwool (£20), plasterboard under (£15), 11mm OSB over (£30), then final roof covering- see below

Total structure- £1120

 

To add to this: vapour barrier (probably <£50); windows/doors (Gumtree?); wall breather membrane (under £100); sundries like fixings, joist hangers etc; final roof covering. EPDM would be a good option, but you'd need to arrange a ventilation space. Could use more steel, at a cost of under £100, plus a bit for the battening etc, and would need to arrange sufficient slope.

 

Insulation is obviously pretty minimal in this design- especially on the roof- this could be improved greatly by visiting secondsandco to get a load of cheap PIR to line out one side of the wall/ceiling buildup.

Edited May 31, 2017 by Crofter
forgot wall membrane etc

[Ferdinand]

OK. A SIPs version.

 

A basic structure to be practical and inexpensive. Obviously there are elephant traps in some places, and other suppliers.

 

1 - Basic building. A SiPs kit from Simply SIPS, which gives an insulated 8x12' kiosk faced with OSB3, with a 5ft wide doorway for £1199. 97mm SiPs with U value of 0.3,

 

 

2 -  Doorway. I will pay between about £600 and £900 for a custom made and fitted PVCu door and glass side panel to a pair of French doors for that gap, including locks and fitting, with a U-value of 1,5 or so. Call it £700.

 

3 - Base. Possibly slabs or fence posts or a concrete slab, Cost not very much unless serious groundworks required. Allow £10-250.

 

4 - Cladding. What does it need? I know that I will pay around £7 per sqm for plastic shiplap-style cladding in white. It comes in 5m x 300mm lengths for £10 which are tricky to carry in a small car. The cabin will look very white from the outside, but be easy to clean.

 

Call it £200 for the cladding, £40 for the laths, £60 for the membrane. 

 

Plastisol coated corrugated may be an alternative for cladding.

 

5 - Roof. It comes with a 1:40 fall towards the back.

 

They recommend EDPM. Say £150 including adhesive etc.

 

6 - Summary

 

Adding up I make that just over £2500 before work starts on the interior and services, if the base is concrete.

 

A different approach to @Crofter for something reasonably insulated, with new materials, and which could relatively easily be dismantled.

 

Ferdinand

 

Edited May 31, 2017 by Ferdinand

[Crofter]

That's very interesting- the SIPS price of £1199 compares to £790 for my BOTE stick build when comparing the same build elements. Not that much of a markup considering the much better performance and quicker build time.

A more detailed costing might drop the price slightly, I've just used gross areas and rounded up where appropriate. If you have large openings for doors/windows then that will be a significant difference to the materials needed.

Edited May 31, 2017 by Crofter
clarity

[Ferdinand]

29 minutes ago, Crofter said:

That's very interesting- the SIPS price of £1199 compares to £790 for my BOTE stick build when comparing the same build elements. Not that much of a markup considering the much better performance and quicker build time.

A more detailed costing might drop the price slightly, I've just used gross areas and rounded up where appropriate.

 

I am inclined to think that they have a big machine they need to run at 100%.

 

Spoke to the chap this morning while doing the post, and they have not yet put up prices due to recent rises. Approx. 10% rise coming.

 

What orientation would your cladding be? H or V?

Edited May 31, 2017 by Ferdinand

[Crofter]

Steel cladding would always be vertical, so you would want to counter-batten.

I paid £10/m2 for my roofing material- 0.7mm thick with 200 micron PVC coating, 20yr guarantee. That's what I based my BOTE prices on. You could go with 0.5mm and a simple galvanised finish and knock a fair chunk off that, if you wanted.

[Ferdinand]

9 minutes ago, Crofter said:

Steel cladding would always be vertical, so you would want to counter-batten.

I paid £10/m2 for my roofing material- 0.7mm thick with 200 micron PVC coating, 20yr guarantee. That's what I based my BOTE prices on. You could go with 0.5mm and a simple galvanised finish and knock a fair chunk off that, if you wanted.

 

I used .7 with a coating for a sun lounge roof for a Tenant which seems extremely good several years later.

 

For cladding I would probably go for the same in expectation of a 20 year life to match the building, unless it was going to be at least half cheaper than the .7 to have the .5 . Even that might be a false economy.

 

It would also need some thought to make it dismantle-able and remantle-able.

 

[mrfish]

1 hour ago, Ferdinand said:

OK. A SIPs version.

 

A basic structure to be practical and inexpensive. Obviously there are elephant traps in some places, and other suppliers.

 

1 - Basic building. A SiPs kit from Simply SIPS, which gives an insulated 8x12' kiosk faced with OSB3, with a 5ft wide doorway for £1199. 97mm SiPs with U value of 0.3,

 

 

2 -  Doorway. I will pay between about £600 and £900 for a custom made and fitted PVCu door and glass side panel to a pair of French doors for that gap, including locks and fitting, with a U-value of 1,5 or so. Call it £700.

 

3 - Base. Possibly slabs or fence posts or a concrete slab, Cost not very much unless serious groundworks required. Allow £10-250.

 

4 - Cladding. What does it need? I know that I will pay around £7 per sqm for plastic shiplap-style cladding in white. It comes in 5m x 300mm lengths for £10 which are tricky to carry in a small car. The cabin will look very white from the outside, but be easy to clean.

 

Call it £200 for the cladding, £40 for the laths, £60 for the membrane. 

 

Plastisol coated corrugated may be an alternative for cladding.

 

5 - Roof. It comes with a 1:40 fall towards the back.

 

They recommend EDPM. Say £150 including adhesive etc.

 

6 - Summary

 

Adding up I make that just over £2500 before work starts on the interior and services, if the base is concrete.

 

A different approach to @Crofter for something reasonably insulated, with new materials, and which could relatively easily be dismantled.

 

Ferdinand

 

If you use this company please keep us up to speed on how it goes.

[mrfish]

Does anyone know anywhere in this country where you can buy a hot knife for gouging out the SIP insulation? If you could lay your hands on one of those you could just buy panels and make the box yourself. I have looked and  can't find one for sale in the UK.

http://www.ebay.com/itm/L-H-Electric-Foam-Scoop-Hot-Knife-SIP-Panel-Scoop-7-25-Wide-750-Watt-NEW-/262944502357?hash=item3d38b6b255:g:GEUAAOSwmCVY9-Er

 

[Jeremy Harris]

I have both a hot knife and a hot wire cutter, both home made.  Not that hard to make, and there are bound to be some tutorials around on the web, as lots of people use them.  I use mine for cutting and carving XPS, when making lost foam composite parts, but EPS cuts just as easily as XPS.

 

It might be worth checking what the foam is in the SIPS, though, as some use PUR foam, and it would be pretty hazardous to try and hot wire cut that, as heating it gives off very toxic fumes.

[Onoff]

I've always thought you could space OSB at 100, 150, 200mm or whatever with long studs and nuts. Then just fill the gap with "pu" foam - the kit sort that comes in the propane like sized cans and is usually used for between rafters. It'd sort of self inflate with the wet foam sticking to the inside face of the OSB. When cured, remove the studs and foam fill the holes.

[Jeremy Harris]

The problem is judging the expansion rate, I think.  I've used two-pack PU foam to fill cavities (boat floatation chambers) and it expands with a great deal of pressure, enough to bow out pretty robust panels if you get it wrong, it also tends to shrink back after it's cured, causing the panels to then bow inwards.

 

I have a feeling that the EPS SIPS panels are made using OSB glued either side of accurately sliced EPS sheets.  I'm sure I've seen a video on the web somewhere of the process.  I reckon that it could be a DIY proposition, using something like a slow cure PU adhesive.  The key would be finding an easy way to apply even pressure to the OSB - EPS - OSB sandwich, as the glue was curing.  Whether it would be cost effective or not I don't know, but it might be. 

[Crofter]

I doubt that a DIY SIP panel would be cost effective. The guys who churn these out all day are set up with the right supply chains and equipment. Unless your own version was going to be in some way different, I don't see where the saving is. A bit like saying you could make your own paving slabs, or concrete blocks.

 

I actually tried making my own I-joists, as I figured I could save some money and it might be fun. The first one was fun as a sort of curiosity, but after finishing the second one I tallied up the cost so far and projected it for the remaining joists- and gave up and bought them in. Cost of saw blades and glue were adding up rapidly, and confidence in the finished product was nowhere near what it would be if bought in ready-made. That's before factoring in my time. The cost of JJI joists was nowhere near high enough to make a DIY alternative viable.

[Triassic]

Ok, the cheap option, over stock SIPs panels from here https://www.secondsandco.co.uk/s-i-p-pannels

 

SIP PANEL 142 MM THICK 1.220 wide x between 7.3 and 7.5 m long ---- £175 each 

 

[Onoff]

I'm thinking more to construct the whole shed as a hollow, two skinned construction then fill with foam. I reckon it could be done.

[Triassic]

 

27 minutes ago, Onoff said:

I'm thinking more to construct the whole shed as a hollow, two skinned construction then fill with foam. I reckon it could be done.

 

Your way will cost you more and be more challenging. Mind you, it'll be an interesting project. You could use polystyrene beads and glue them in place, might be easier and cheaper.

Edited May 31, 2017 by Triassic

[Crofter]

What about straw bale? Depending on your attitude, and the proximity of other buildings, the fire risk might not be an issue for a building in which nobody is supposed to be sleeping- you just take the risk. But the loss of floor area would be a big deal, and the building would no longer be dismantlable. 

[Jeremy Harris]

19 minutes ago, Triassic said:

 

 

Your way will cost you more and be more challenging. Mind you, it'll be an interesting project. You could use polystyrene beads and glue them in place, might be easier and cheaper.

 

Good idea.  Blown bonded beads might be good enough, and are pretty cheap.  I'm pretty sure they are blown with a coating of PVA, and it may well be possible to increase the amount of PVA, so that they bond securely to the OSB skins.  The bond strength doesn't need to be massive, as the loads on the foam are very low, it's only stopping the OSB sheets from crippling under the compressive load.

[SteamyTea]

I did this a few years ago for a giggle

 

[Onoff]

1 hour ago, SteamyTea said:

I did this a few years ago for a giggle

 

 

That was YOU! Saw the link on the GBF.

[MrMagic]

For info/inspiration here's something that I'm just in the process of finishing up - my garden shoffice (half shed, half office)

 

Wall construction was (inside to out) - 

- 11mm OSB

- Multifoil insulation (I was curious to see how well it worked..)

- 4x2 stud filled with 100mm Knauf Ekoroll

- 9mm OSB

- Breather membrane

- Horizontal batterns

- Vertical cladding (gravel boards "good" side facing out)

 

(there should be more air gaps and such, but it's a shed at the end of the day...!)

 

Roof is EPDM on 18mm OSB, 4x2s @ 600 centers, mix of ekoroll and celotex, 11mm OSB internal finish

 

Floor is 18mm OSB on 6x2s @ ~400 centers. Ekoroll supported by breather membrane looped over the joists

 

Costs add up surprisingly quickly but saved money by sourcing all the joists from a nearby bungalow that was being scalped and turned into a house - the builder said it's a shame as it all treated, slow grown, dead straight wood but because it isn't graded he has to burn it or skip it. All the joist wood cost me £20 + labour for denailing etc.

 

Smallest 9000btu ASHP for heating

 

Still needs some finishing touches and another coat of paint/stain (Cuprinol Shades) but otherwise it's probably very close to what you're trying to achieve.

 

[Ferdinand]

The different time vs cost balances are interesting.

 

For me quick assembly would be quite important quick.build - ideally just a 2-3 days - as I would be paying someone and effectlively being the 'mate', and that would tip the balance towards the SiPs version.

 

F

[Ferdinand]

On 2017-5-31 at 20:23, Triassic said:

Ok, the cheap option, over stock SIPs panels from here https://www.secondsandco.co.uk/s-i-p-pannels

 

SIP PANEL 142 MM THICK 1.220 wide x between 7.3 and 7.5 m long ---- £175 each 

 

 

That is quite interesting. £20 per sqm for 6" insulated panels, even at weights of perhaps 200kg+ each. Assuming you can move them and handle them could be a good idea.

 

Put it on a suitable support and just cut off the lengths you need for your next building with the mother of all circular saws. What would you cut these with?

 

Adding it up, the SiPs for the 8x12 I discuss above, leaving the gap for the door, are £940 at £20 per sqm.

 

= Perimeter is 12ft + 8ft + 8ft + 7ft (5ft door gap)

Plus 12ft length for roof + 12ft for Floor

All x 8ft = (35 + 24) x 8 = 590 sqft = 59 sqm ==> £1180 for the panels before any wastage etc and wooden framework required etc.

 

It is true that the panels are better, but the price just for the raw secondhand panels is the same as the whole kit.

 

Very tempted by one of those kits. Look to be incredibly tightly priced.

 

Ferdinand

Edited June 2, 2017 by Ferdinand