Friday 8 July 2016

Nailed Down

Clearline Fusion integrated solar installed by Go Green Systems.  Image (C) Go Green Systems

Change to UK Roofing Standards with Consequences for Solar

The British Standard for slating and tiling (BS 5534:2014) was updated in August 2014, and after a period of overlap to allow industry to finish jobs already started the previous version was withdrawn in February 2015.

Although the building regulations do not specifically call it up, most manufacturers of tiles and slates make sure that their installation guidelines closely follow the standard.  In addition, architects and designers will use it in their specifications and providers of insurance warranties to housebuilders such as NHBC require that tiles and slates are installed in accordance with the standard (for example, see section 7 of the NHBC technical document). 

The bottom line is that most new roofs in the UK will now be installed to this standard and the changes have some impact on the installation of solar on these roofs.

Fixing of Underlay

The underlay resists a proportion of the pressure difference created across the roof by wind.  If it is insufficiently well secured, it can balloon up and press on the underside of the tiles or slates.  New guidance in the standard describes how the laps strips of underlay should be secured - either by covering the bottom edge of the lap with a batten or sealing between the laps with double sided adhesive tape.

Solar wiring is often passed through into the building by passing the cables up between the laps in the underlay.  However, the double sided tape used to  stick down the laps is so effective it can't be peeled without tearing the underlay.  Installers might be tempted to cut through the underlay to pass cables through instead of taking the more time-consuming option of running them up to the top of the roof and into the building through the ridge vent.

No Tile Without a Nail

BS5534:2014 has an updated wind speed map, in which the wind speeds have increased compared to the previous version. This apparently reflects the greater likelihood of extreme weather events in a warming planet, and aligns more closely with European standards. 

Whatever the reason for this change, the outcome is that where previously only single-lapped tile roofs in highly exposed locations would need to mechanically fix every tile, now pretty much every roof is going to have every single tile nailed, screwed or clipped down to the tile battens.

For a roof that has been laid in this way, the task of retro-fitting an above-roof solar system has just got much more difficult. 

With a loose-laid roof (perhaps with only every fourth course of tiles fixed) you could simply slide tiles up and under the row above to fix brackets to the roof structure below.  This trick is also often used to provide foot-holds on the roof and avoid the risk of cracking tiles by walking around on top of them. 

For a roof built to the new standard, this option isn't available.  Real care is going to have to be taken to avoid the risk of damaging the roof covering so access to the roof is likely to need to be on boards or roof ladders.  Removing and replacing tiles for fixing roof hooks is going to be significantly more time-consuming, perhaps involving ripping nails to remove  a patch of tiles for each roof hook and using adhesive to replace that final tile (since it's impossible to nail).  Installers  may find that removing a large area of tiles and replacing them with a roof integrated solar system is far less trouble.

As the years go by, to stock of homes in the UK that have been built or had their roofs re-laid since the standard was updated will slowly increase.  It will become less and less of a sure thing to assume that the roof of the building you are quoting to install on will have loose laid tiles.  Solar installers should be particularly wary when pricing jobs on homes that have clearly been built in the last couple of years.

Of course for those solar installers that operate in the new build market the impact of the change is immediate.  With a loose-laid roof it was previously possible to install an above-roof solar system on a new home just like a retrofit on an existing one.  Occasionally the roofing contractor would refuse to provide a warranty on a roof if a solar installer had been tramping round on top of it lifting and notching tiles to fix roof hooks behind them.  Then it might be necessary for the build programme to allow time for the solar installer to fix roof hooks after the roofer had battened the roof but before they had tiled it.  This now becomes the only way to work with a nailed roof and clearly requires an additional visit to site for the installer. 

Even then, when you come back to fit the rails and modules above the tiles you need to figure out a way to get the cables through  into the building.  The cheapest option is push the cable up through a notch cut in the back of the tile (hopefully with some protection against abrasion of the insulation such as a flexible plastic conduit).  Alternatives include a flashing with cable glands or a similar cable entry created with lead.  All these options are extremely awkward to install without being able to easily remove the tiles fixed down by the roofer.

Little wonder that with the advent of cost-effective roof integrated solar that has closed the gap in cost with above-roof kits, most solar installers working in the new build sector have decided that roof integration is the only way forward.  Not only are the aesthetics more acceptable to customers it's now just so much less hassle to install.  It needs only a single site visit to fit the system after which the roofer can fit the slates or tiles all around using as many nails as they like!


Thanks to Etienne Hilaire  Avonside Renewables for their advice on the practical impact of the new standard.