Fixing insulation query

[Keeplearning]

Hi. We are up to roof joist height on our modern new-build in Lincolnshire and have not yet decided which flat roof system to use (sarnafil, EPDM or GRP?). The house will have an insulated external render system (Sto) with 200mm EPS insulation. We are keen for the roof to have similar thermal properties. I would be really grateful to hear from anyone who has experience or ideas about how we fix 150 - 200mm of insulation on the flat roof, as most mechanical fixings are not long enough to go through the full thickness of insulation. We also haven't yet decided which type of insulation to use - there is a bewildering choice! The total roof area is approximately 200 square metres.

The logical solution seems to be to use adhesive to fix the insulation onto the base decking board, to sandwich 2 layers of insulation together with adhesive, and then to use adhesive to fix the top decking board onto the insulation - like a big sandwich. This will hopefully reduce lift, although we have been advised this should not be too much of a problem as the house has a parapet around the roof. Any advice or comments would be gratefully received.

 

[freddiemercurystwin]

How are you getting the fall, is the insulation tapered or flat, is the base a structural steel deck or timber (plywood) or concrete? Mechanical fixings are the only sure way to go IMO. Also gluing a vapour control layer in between the insulation and the deck just seems daft. If you did go the adhesive route and happened to get a duff batch of glue the whole roof would be fecked.

 

[SurreyRoofingEstimator]

The way we do it is to use a plastic tube fixing, for a 200mm thick insulation this would require a 180m tube and 75mm fastner. The same tube system in a mech fix single ply system are used to fix the laps

Click this link to see what I mean http://www.flatroofingsupplies.com/FRS-Global_Fastening_System.shtml#Global

 

[Keeplearning]

Wow, can't believe how quickly I've had some replies - many thanks.
The fall will be created by timber firrings that our joiners will build in when they fit the joists. The insulation will therefore be flat. The plan is to use a timber base deck (18mm T&G chipboard probably), as well as a timber deck (18mm chipboard or OSB) above the insulation to allow it to be walked on.
I see what you mean about the problem of using adhesive, it is just that I haven't been able to find a mechanical fixing that will cope with 200mm of insulation. Where would I source the tube and fastener system?

Please excuse my ignorance but I'm just a humble school teacher/mum who is trying to project-manage a very complex build! I'm doing my best to understand the processes involved so that I don't get hoodwinked and bull****ed to by trades (sadly not all seem 100% competent and upfront).

I dont' suppose you have any suggestions about which roofing system I should go for - Sarnafil, EPDM & GRP being the main choices?

Really appreciate your help with this.

 

[Keeplearning]

Thank you for the link, SurreyRoofingEstimator, for some reason it didn't come up when I first viewed your reply.

 

[freddiemercurystwin]

Personally if you can afford it a single ply is the way to go, Sarnafil being a good choice. There are various kinds of fixings out there eg http://www.twistfix.co.uk/products/insulation-fixings/insulation-fixing-anchors-zp-product.html

Don't under any circumstances whatever you do use chipboard under or above your roof, plywood only! Should you happen to get a good downpour on the day they fit the first deck the whole lot will be ruined, let alone you ever get a leak in the future.

 

[Keeplearning]

Thank you, Freddymecurystwin, I will heed your wise advice and stay clear of chipboard. What about OSB3? Also should the decking board be T&G or is it OK to butt-join straight-edged board? I'm not sure what people normally do, and T&G is more expensive.
Carry on like this and I could almost kid myself I know what I'm talking about!
Thanks again for taking the time to respond.

 

[freddiemercurystwin]

You could use OSB roofing grade although not as good as plywood IMO but then it is cheaper. No need to have T&G provided all joints are fully supported and its fitted well. Must be WBP plywood if you opt for that.

You know that you probably don't need the plywood above the insulation (depending on the insulation choice) and you opt for single ply BTW?

 

[Keeplearning]

The reason for the ply above the insulation is to reduce the risk of compression as the roof will need to be walked on to access/clean 2 rooflights. Perhaps we would get away without a ply top deck here? However, we also have one area of balcony that will hopefully have lots of use sunbathing in our glorious british weather!

 

[freddiemercurystwin]

As mentioned for general maintenance/access for cleaning a ply deck is not required just adhesive or mechanically fix the single ply to the insulation. For a terrace you should be fitting something down to protect the single ply like decking or paviours anyway. It will not stand up to the riggers of chair legs or heels etc.

 

[Keeplearning]

I plan to put a wearing surface on top of the membrane on the terrace/balcony (decking or tiles), but assumed that I would still need to have a top-deck. For example, we have been advised to use Kingspan TR27 by a sarnafil fitter who is providing a quote, and that insulation doesn't have a bonded ply top layer. Surely we would need something rigid under the membrane? It would be great to save money by not having a top-deck, but I don't want to create problems in the future by cutting corners.

 

[freddiemercurystwin]

Provided spreader plates like this http://www.wallbarn.com/plastic-fixed-height-support-pads.htm were used on a protective membrane to support your slabs and the insulation is designed for the purpose then plywood will not be required. It won't do any harm if you really want it Provided it doesn't restrict the drainage but is not required by the manufacturer to maintain the warranty, hope your structure's been designed as floor rather than a roof.

http://www.roofassured.co.uk/drawings/pdf/2.8 Mechanically fixed upstand terminated into chase.pdf

 

[cotswoldbuilders]

We use osb strand t&g boards, with Firestone epdm rubber fully bonded to decking, cut to size, no joins.
With this system you have the option of Walk Way pads, that can be loose laid or glued to rubber.
You can also lay paving on the rubber roof via special discs that take 4no corners of paving slabs.

 

[Keeplearning]

Thank you everyone for the really good advice. Has anyone experience of GRP roofing - either positive or negative?

 

[cotswoldbuilders]

We have done quite a few of these years ago, an Esterseal Resin roofing system, to be quite honest Im not really impressed with glass fibre roofs.
They look good when first fitted, but if matting and resin hasnt been put down correctly small pin holes can occur, causing the glass fibre to delaminate.
When we read the small print, regarding gaurantees the onus would always fall back on the fitter, ie if done on a hot day and you sweat the manufactures would say, that was the cause of delamination.
Try walking on them in frosty weather, you can hear them creaking.
We researched the epdm, and can confidently give a 25yr gaurantee on this system, life expectancy at least 50yr.
Having said that, some pour and roll roofs we have done are still in good condition.
Im not slating glass fibre roofs, as if fitted properly will last well.