Typical details

Ridge

The ridge detail must be carefully designed and installed, and is potentially a weak point in preventing water ingress on a very flat roof. The Secret Fix system is designed to operate on roof pitches as low as one degree (actual measured pitch) therefore it is possible for wind driven water to actually move up the roof pitch dependant on the roof aspect. Clearly therefore the ridge needs to be a robust detail. By utilizing a specially shaped ridge filler, the pan of the sheet is completely damned to prevent ingress of water, and as a second line of defense the pan of the sheet is turned up behind the filler. The ridge flashing attachment is designed to maintain the fundamental purpose of the system, having no penetrations of the building envelope - all the flashing fixings are outside of the building envelope.

Eaves

Due to the potential very low pitch that the secret fix roof system can be used at, it is important to ensure that water cannot track back under the end of the sheet by surface tension. Therefore the end of the sheet is turned down to create a minimum 15 degree angle (although it is normal to turn the sheet down more than this) and form a natural drip point. This is reinforced with a drip angle fixed through the pan of the sheet (outside of the building line), and an eaves filler is used to prevent ingress of vermin.

Verge

The overlap edge of the sheet must be supported, and a penetration free detail is required, therefore the use of the secret fix verge support gives one component to do both jobs, and allows the verge flashing fixing to be outside of the building envelope.

Rooflights

Triple skin GRP rooflights are normally used within a secret fix system, either as an in-plane system (for roof pitches over 5 degrees) or a barrel-vault system. The liner must provide the required non-fragility for the system, both during construction and throughout the life of the building. A clear polycarbonate intermediate layer is used to enhance the thermal performance of the rooflight system. It is normal to use rooflight closure flashings either side and top and bottom of a rooflight in order to conceal the quilt insulation. Vapour control is provided by sealing the liner in the normal way. It is important that rooflights are not laid out in a checker-board pattern, and in-plane rooflights must start at the ridge. Barrel-Vault rooflights require flashings back to the ridge upslope of the rooflight, and for both rooflight solutions require care during installation to maintain matching cover of the liner and outer sheet profiles - if creep occurs this could cause mis-aligned rooflights.

Roof Penetrations

Can either be small penetrations (for flues, vents, soil pipes etc) or large (for smoke vents, access hatches, dome rooflights). Small penetrations are normally dealt with by using a small bolt-on soaker unit, usually off-the-shelf systems. Large penetrations need to be carefully detailed to allow up-slope rainwater to drain around the penetration, and usually involve a bespoke soaker fabrication, or a site applied GRP weathering solution. Site welded soakers are not possible with coated steel roof systems.As noted above, access hatches can be used with secret fix roof systems, however the weathering detail around the hatch needs to be carefully considered and is likely to vary from project to project.

Fall Arrest Systems

Inertia posts and similar fall arrest systems are easily incorporated onto secret fix roof systems, and non-penetrative options are available. Many such systems do not require securing back to the structure of the building, and can attach directly to the outer sheet. Please refer to your fall arrest system supplier or speak to our technical department for our recommendations.

For more information visit our reccomended fallarrest system partners.
www.latchways.com

Safety Walkways

Most secret fix roof systems will allow a certain amount of direct foot traffic, however for regular maintenance traffic or where significant loads may need to be carried onto the roof, it may be wise to install a safety walkway to direct maintenance foot traffic and reduce the risk of trips and falls. Please refer to your safety walkway supplier, or speak to our technical department for our recommendations.

For more information visit our reccomended safety walkway system partners.
www.mrsiteservices.co.uk