Eaves detailing products offer multiple solutions

Manthorpe explores the considerations specifiers must take into account when designing roof eaves to ensure a strong, stable build without water ingress or condensation issues.  

The roof eaves is the lowest area of a pitched roof and, as such, it must shed all the water that the roof collects over its entire surface into the gutters. It is important to design and construct the eaves correctly, to ensure that it will remain durable and prevent water ingress into the structure. A secondary function of a roof eaves is to provide a ventilation air path into the roof void to control condensation. 

Given the importance of the eaves, it is surprising how often their design and construction is poor, leading to leakage problems, sometimes straightaway or, more commonly, later when components degrade. 

Important elements to consider when designing the eaves are ensuring proper support for the underlay and correct alignment of the eaves course tiles. In a typical UK cold roof construction, the underlay is laid unsupported between rafters, which are generally set at up to 600mm centres. This is fine for the general roof areas, but continuous support must be provided behind the fascia or tilt fillet to prevent the underlay sagging and creating a trough which could collect and hold water. If water does collect behind the fascia, it will inevitably find its way through any small cuts or nail holes in the underlay and into the structure. Longer term the underlay will rot, causing further leakage. Modern, lightweight, vapour and air permeable underlays are not UV-resistant in the long-term, so they should not be draped into the gutter as was the practice with bituminous underlays. 

Consideration should also be given to the correct alignment of the roof tiles, particularly when using single-lap tiles. The eaves course tiles should be set at the same angle as the tiles in the roof areas above. If they are not, then the risk of water ingress through the tiling is increased. 

Ensuring proper ventilation  

Traditionally, underlay support was provided by a timber detail, usually plywood. However, in modern construction, time and cost efficiencies are key objectives, and the best way to achieve these are by using well-designed proprietary products. Manthorpe has more than 35 years of experience developing roofing products and solutions that deliver benefits to the construction industry. Regarding eaves detailing, our design team has come up with our 2-in-1 Ventilator and 3-in-1 ventilator products. 

These products combine an underlay support tray, to prevent the underlay sagging behind the fascia, with an over fascia ventilator and insect grille under the support tray to provide 10,000mm2 per metre of air flow into the roof space. The insect grille prevents access into the roof void by nesting insects. The 3-in-1 ventilator has the addition of an integral eaves comb filler to prevent access into the roof void by birds and rodents when using profiled roof tiles.  

The support tray is sufficiently robust to properly support the underlay, while the front edge is angled to aid water run-off into the gutter and is thickened to provide a robust support for the eaves course tiles. There are clear and stable fixing points into the top of the fascia, with drainage gullies around each point to prevent water ingress. Further fixing points are incorporated for secure fixing to the rafters. The support tray is wide enough for use at low pitches and is ingeniously designed with a live hinge between the front edge and support tray to enable the ventilators to be used on all roof pitches from 15° up to 70°.  

The 2-in-1 and 3-in-1 ventilators are suitable for use on refurbishment projects as well as fast installation on new buildings. They are supplied in a one-metre coverage length for ease of estimating and ordering, plus side interlocks to provide fully supported overlaps between each unit. 

One objection to the use of a ventilated eaves support system is that additional ventilation may not be deemed necessary due to the type of permeable membrane. However, just as with dry ridge systems, the ventilation element of these products is a bonus; using the 2-in-1 or 3-in-1 ventilator is still far more cost effective in supporting the underlay than purchasing plywood, with all the additional labour and time in cutting it to fit and installing it. 

Another objection to the use of proprietary underlay support products is the perceived difficulty in the retro fitting or cleaning of gutters. However, this is not the case with the Manthorpe 2-in-1 and 3-in-1 ventilators. Properly fitted, with the gutters installed in the correct position, the ventilators do not impede access to the gutters in any way. 

A feature of the 2-in-1 and 3-in-1 ventilator is that the underlay can easily be taped to the underlay support tray to stop the underlay flapping in the wind – a common occurrence with lightweight underlays. If the underlay does not have integral fixing tape, then double-sided underlay tape can be used. 

An important point to address is that of the fixing of the eaves course tiles; BS 5534 requires that all single lap tiles be twice fixed at perimeters. How this is achieved depends on the type of tile and the calculated roof tile fixing specification. Tiles with two nail holes can be head nailed to satisfy the requirement for two fixings. However, if the tiles only have one nail hole, or twice nailing is insufficient to resist the calculated wind uplift load, then the tiles must be clipped at their tails.  

Tile eaves clips are generally nailed into the top of the facia or tilt fillet, which means the nails having to penetrate the underlay support tray. This is generally accepted as a small compromise in ensuring that the tiles are adequately fixed. However, for an extra layer of protection, bituminous nail tape can be run along the fixing points, which will seal around the nails and thus prevent water running through the nail holes. 

Manthorpe 2-in-1 and 3-in-1 ventilators provide a quick to install, economical, robust solution for roof eaves in refurbishment and newbuild projects.  

www.manthorpebp.co.uk