BucksDad Workshop Build

[BucksDad]

Whose putting the cladding on?
Put aside another day for the chippie to do that too???

I can do the cladding. If building a timber frame building from scratch, that's a lot of work. Should be able to get the panels together in one day... another day for cladding is not so bad.

I can understand the temptation to design and build your own, but you then have all the hassle and risk of making it work.

Before you hit the go button you may like to look at buying a complete insulated building (eg: home office) which could be quickly installed on a prepared base.

Cost may be little different to the diy approach. If there are problems (water ingress etc) you have someone to blame and (probably) a guarantee. They will buy materials in bulk, have a proven (one hopes) detailed design and construction process, ability to install and sign of electrics etc..

Far too expensive to do that and I can't see the value they add. I have effectively got someone to design it... gave them the dimensions and they've done the drawing and sent over a Sketchup 3D model which seems fine. A SIPS panel design & construction is about as simple as you can get.

 

[Molynoox]

In the design you had done in SketchUp is that SIPS based? I would be interested to see it if you could post a picture? I'm interested in the roof mainly, I'm curios how they span across 3 or 4 metres, or more, with SIPS.
Martin

 

[BucksDad]

In the design you had done in SketchUp is that SIPS based? I would be interested to see it if you could post a picture? I'm interested in the roof mainly, I'm curios how they span across 3 or 4 metres, or more, with SIPS.
Martin

They didn't include a detailed diagram but here is a link to a PDF from elsewhere which has span tables and how they're done

SBS design guide - proof 20 (sipbuildingsystems.co.uk)

For garden buildings it seems to be timber ring beam and 400-450mm wide panels with timber joists

 

[Spectric]

I'm curios how they span across 3 or 4 metres, or more, with SIPS.

Look at the design of a trussed roof, these can span the outer walls of a building with no interior load bearing walls and do 10 metres.

 

[Jameshow]

They didn't include a detailed diagram but here is a link to a PDF from elsewhere which has span tables and how they're done

SBS design guide - proof 20 (sipbuildingsystems.co.uk)

For garden buildings it seems to be timber ring beam and 400-450mm wide panels with timber joists

Nice to read some design tables.

The difference of reinforced to unreinforced isn't much at all. 3.6m is quite a span for 150mm

What loading did you specify?

 

[Molynoox]

Look at the design of a trussed roof, these can span the outer walls of a building with no interior load bearing walls and do 10 metres.

And how is that relevant? Totally different materials and design. Flat roof being the key difference.

 

[Molynoox]

They didn't include a detailed diagram but here is a link to a PDF from elsewhere which has span tables and how they're done

SBS design guide - proof 20 (sipbuildingsystems.co.uk)

For garden buildings it seems to be timber ring beam and 400-450mm wide panels with timber joists

Cheers
That was an interesting read, the span tables are pretty impressive, I didn't realise they were that strong. I know that the kingspan roof panels you can buy are similarly strong and they are quite similar to SIPS except they have a metal skin. So I shouldn't be all that surprised I suppose.
4 or 5 metres is adequate for most flat roof garden buildings.
Martin

 

[Spectric]

Flat roof being the key difference.

In my opinion something to be avoided, at least put some slope it one way and it will last a lot longer.

 

[Molynoox]

In my opinion something to be avoided, at least put some slope it one way and it will last a lot longer.

Agreed. Typically 1 in 40 is used for detached buildings like this, in reality flat roof is shorthand for 'slightly sloped' - that's what I meant anyway, and I know that's misleading hence the clarification

 

[BucksDad]

Yes I think my design has a 1:60 slope. Looking at those span tables with 150mm roof and the suggested typical loadings - 0.5 DL, 0.6LL that puts the span at 4.25m so as I have a span of 3m that should be plenty.

Interestingly I checked my quote again and they specified 100mm panels for the roof - I've gone back to them and queried it as that just doesn't seem right - no reply as yet. In the meantime I've asked for a quote from supersips.uk.com who publish all the accreditation.

Interestingly they also publish the insulation values for their roof and condensation analysis. I've read up and a SIPS roof is a cold roof, so typically with a house, should be ventilated. Garden rooms obviously etc. they just slap the EPDM on the OSB.

"Interstitial condensation occurs but all the condensate is predicted to evaporate in the summer months" - sounds like a nice little get out clause there

Having thought some more, I'm considering the need for a single room MHVR anyway because a SIPS box does produce a very air tight design

 

[Inspector]

SIP panels can't be looked at in the same way as a traditional framed assembly. The skins and foam act as one much like honeycomb panels in aircraft do. The sum of the parts are stronger than the individual ones are. Example. A camping cooler holding your beer and burgers has a lid of flimsy plastic and foam that individually would collapse if you sat on them but because the skins are bonded to the foam core you can easily sit on them and even do a little dance on them when you've finished the beer. That is why SIP built structures are engineered to fit the situation. If they say the 100mm panel is strong enough for the roof they will be.

Pete

 

[Jones]

Flat roofs used to have very low slopes 1 in 80 etc as this allowed protective gravel to be laid over felted roofs,( and dirt, moss etc to accumulate). The fashion nowadays is to have a steeper slope to drain faster and wash off debris like 1 in 40 ( 25 mm per metre). The dead load is the weight of the structure in this case the roof, the live load is any additional load that may be added, such as someone on the roof to repair it or more importantly snow. In building regs the standards are snow load of 0.75 throughout most of the UK and 1 kn/m2 in the high snowy bits. Engineers can argue for a lower value so 0.6 may be ok for you but worth checking how they choose that value.

 

[Jameshow]

Yes I think my design has a 1:60 slope. Looking at those span tables with 150mm roof and the suggested typical loadings - 0.5 DL, 0.6LL that puts the span at 4.25m so as I have a span of 3m that should be plenty.

Interestingly I checked my quote again and they specified 100mm panels for the roof - I've gone back to them and queried it as that just doesn't seem right - no reply as yet. In the meantime I've asked for a quote from supersips.uk.com who publish all the accreditation.

Interestingly they also publish the insulation values for their roof and condensation analysis. I've read up and a SIPS roof is a cold roof, so typically with a house, should be ventilated. Garden rooms obviously etc. they just slap the EPDM on the OSB.

"Interstitial condensation occurs but all the condensate is predicted to evaporate in the summer months" - sounds like a nice little get out clause there

Having thought some more, I'm considering the need for a single room MHVR anyway because a SIPS box does produce a very air tight design

How about a simple double tube as found on a combi boiler balanced flu where the new air flows dow the one tube and the waste air out the inner tube? A swiveling cowl on the top would make it work better as would some alu electronic heat sinks bolted though the inner tube to increase thermal conductivity....?

 

[Molynoox]

Yes I think my design has a 1:60 slope. Looking at those span tables with 150mm roof and the suggested typical loadings - 0.5 DL, 0.6LL that puts the span at 4.25m so as I have a span of 3m that should be plenty.

Interestingly I checked my quote again and they specified 100mm panels for the roof - I've gone back to them and queried it as that just doesn't seem right - no reply as yet. In the meantime I've asked for a quote from supersips.uk.com who publish all the accreditation.

Interestingly they also publish the insulation values for their roof and condensation analysis. I've read up and a SIPS roof is a cold roof, so typically with a house, should be ventilated. Garden rooms obviously etc. they just slap the EPDM on the OSB.

"Interstitial condensation occurs but all the condensate is predicted to evaporate in the summer months" - sounds like a nice little get out clause there

Having thought some more, I'm considering the need for a single room MHVR anyway because a SIPS box does produce a very air tight design

that's a very interesting quote you found about the interstitial condensation - I had been thinking about that and I wondered if the OSB bonded to the foam core would provide a suitable barrier, when combined with a suitable vapour barrier. I also wondered if the SIPS would be considered to be a warm roof but you also mentioned earlier it is considered as a cold roof. I suppose the difference is that in a warm roof the insulation is continuous and in the SIPS.... do you have timber supports between panels? i know very little about SIPS but I thought I had seen pictures of SIPS where the OSB just interlocks with insulation panels butted up against one another which would mean that the insulation was continuous without any thermal bridging from studs. Or is it cold roof because the insulation doesn't sit outside of the roof structure, maybe its that simple. I'm probably overthinking it
Martin

 

[BucksDad]

SIP panels can't be looked at in the same way as a traditional framed assembly. The skins and foam act as one much like honeycomb panels in aircraft do. The sum of the parts are stronger than the individual ones are. Example. A camping cooler holding your beer and burgers has a lid of flimsy plastic and foam that individually would collapse if you sat on them but because the skins are bonded to the foam core you can easily sit on them and even do a little dance on them when you've finished the beer. That is why SIP built structures are engineered to fit the situation. If they say the 100mm panel is strong enough for the roof they will be.

Pete

I think you place too much trust in our country Pete. As I can build this under permitted development rights without any need to inform anyone what I'm doing, there's no need for me to certify what I'm doing. I've noticed the original company I got the quote with state their SIPs are for workshops, garden rooms etc. only. At the end of the day, a SIP panel is just some insulation glued between some OSB - anyone could make one.

I seriously doubt that SIPs panels can span 3m with 75mm / 3" rafters and not suffer from deflection long term. The fact no other SIP manufacturer has published a span table with anything less than 150mm for the roof tells me all I need to know I think

 

[Glitch]

Or is it cold roof because the insulation doesn't sit outside of the roof structure, maybe its that simple.

AIUI it is that simple. Insulation on the inside of the OSB makes it a cold roof. It'll need suitable ventilation.

I made a mistake with my (over-engineered) shed and put OSB on both sides of the insulated studwork. I'd copied a couple of builds I'd followed on YouTube.
That was before I discovered Mike G's shed build guide.

However, Mike uses OSB as a vapour barrier in his design. OSB is not a proper vapour barrier. It's not impermeable but in his design there is nowhere for the vapour to condense, which is good. I installed a vapour barrier (plastic sheeting) on the inside of the stud work with OSB over it. Bit of a minefield but I doubt the shed is going to have hot sweaty, vapour breathing people in it much.

 

[Glitch]

Another thing to bear in mind is sheet materials for some bizarre reason are 8' x 4' (2440mm x 1220mm) so make sure you do the studwork at 16" or 24" on centre, or you'll find you'll need to cut every board. Check the sizes carefully because some stuff, comes only in metric! I think I ordered some 9mm boards that only came in 2400mm x 1200mm.

 

[Molynoox]

Flat roofs used to have very low slopes 1 in 80 etc as this allowed protective gravel to be laid over felted roofs,( and dirt, moss etc to accumulate). The fashion nowadays is to have a steeper slope to drain faster and wash off debris like 1 in 40 ( 25 mm per metre). The dead load is the weight of the structure in this case the roof, the live load is any additional load that may be added, such as someone on the roof to repair it or more importantly snow. In building regs the standards are snow load of 0.75 throughout most of the UK and 1 kn/m2 in the high snowy bits. Engineers can argue for a lower value so 0.6 may be ok for you but worth checking how they choose that value.

are you taking that 0.75 value from Part A?

 

[Dave Moore]

Hi,
If you look on YouTube for Steve @Londonflatroofing he has some very good videos on flat roofing including warm and cold roofs. I emailed him last Monday and within half an hour he had sent me a video with advice on my build.
Regards,
Dave

 

[Molynoox]

Yeah Steve is awesome.