Part 3 of the four part Guide To Roof Construction covers pitched roof detail: roof ridges and ridge tiles, roof hips and hip tiles, roof valleys, roof verges and lead flashings. To get the most out of it is helpful to also read Parts 1 and 2.
Part 1 – A Guide To Roof Construction covers an overview of flat and pitched roofs.
Part 2 – Pitched Roof Construction covers pitched roof materials, basic pitched roof designs, cold and warm pitched roofs and pitched roof construction.
Part 4 – Flat Roof Construction: covers flat roof materials and flat roof construction of warm and cold roofs.
Where the two sides of a roof meet is called the ridge. To ensure that this is watertight a ridge tile is used to cover the gap. This can be bedded with mortar or a dry fixed ridge system can be used. On some types of ridge tile the mortar bedding will not be visible on the outside of the tile – the mortar bedding will be on the inside of the ridge tile. When there is no mortar visible on the outside of a ridge tile then this is not necessarily a cause for concern in itself – despite what some rogue roofers may tell you.
The joints between each of the ridge tiles are also filled with mortar.
A variety of ridge tiles are available. These include:
- Half Round Ridge Tiles
- Third Round Ridge Tiles
- Angled Ridge Tiles
- Collared Ridge Tiles – these are made to interlock with each other with a slight overlap
- Ornamental Ridge Tiles
A hip roof can either use ridge tile which are mortared in place or uses special tiles called hip tiles.
When using ridge tiles a hip iron is often used to prevent the tile from falling if the mortar fails. The hip iron is fixed onto the timber and then is used to help retain the mortared ridge tile at the bottom of the ridge. The hip iron should protrude above the tile.
There are two types of hip tiles generally used, Arris hip tiles as shown above and Bonnet hip tiles that have a raised area (that looks like a rounded car bonnet or a ladies bonnet).
As well as hips and gables roofs often feature valleys. These are the joins between two roof areas.
Valleys can be constructed in a number of ways, using:
- Valley tiles which allow the roof to be continued round corners ( they are special tiles which are the opposite of a hip tile really). They can only be used when the pitches of the two roofs are identical.
- An open valley, often 100mm or 150mm wide with a metal (normally lead) or sometimes a GRP lining. The valley is a drainage channel below the level of the roof which is constructed of wood with the lead to provide the waterproofing
- A closed valley with a pre-formed GRP strip. As in the lead valley example any water drains into the GRP strip and then down into a gutter.
All three types of construction can be attractive. In the photo above two of these roofs need repairing. The GRP closed valley roof has just been refurbished. The attraction of the valley tile is that each level of tile can sweep round the roof (the layers of tile on the left of the roof are continued on the right). With the lead lined or GRP valleys then the tile layers on both sides are not always aligned. It is not always possible to align both sides of a valley if the roof pitch for the two roofs being joined are different anyway. The lead valley shows one of the disadvantages of this type of valley; the tiles are not always supported and can slip into the valley. Nowadays a valley tile or the GRP strip are preferred; not least as lead is expensive and does not last any longer than GRP. Lead valleys normally use code 4 lead and strips should be overlapped with no strip longer than 2m with overlap (1.5m will be visible). This is because lead expands and contracts with changes in temperature and a longer strip will crack.
The edge of a pitched roof as it meets the gable end is called a verge. Tiles here are normally fixed in some way to prevent wind and rain from getting underneath the tiles. Often the end tile of each row is mortared into place as shown below. Dry fix options for verges are also available from a number of manufacturers.
Lead is still used as a roofing material as part of the seal between any brickwork and the roof.
The lead flashing goes underneath the tiles and then is recessed into the mortar joins of the brickwork. It is then fixed into place using mortar (not shown in picture). A flashing for a chimney on a hip roof consists of four elements:
- Front apron – the join between the bottom of the chimney and the guttering, made of code 4 lead
- Soakers – used on the side of the chimney. These are small rectangles of lead that are hidden in the image above. They sit under the lead step flashing and the tiles closest to the chimney. Code 3 lead is used as thicker lead would push the tiles up too high.
- Step flashing in code 4 lead covers the soakers and the brick side of the chimney
- Back gutter in code 4 lead . Water falling behind the chimney need to be drained to the sides. Getting the back gutter right is a key part of waterproofing round a chimney, otherwise the water can just sit there.
On a chimney positioned on a ridge then there is no back gutter, just two front aprons.
To read about flat roof construction go to Part 4 – Flat Roof Construction: this covers flat roof materials and flat roof construction of warm and cold roofs. Otherwise we hope this guide to roof construction has introduced you to some of the basics about roofs. This should equip you with some knowledge when you discuss roof repairs and replacements with a roofing contractor. To take things further you can explore more about different types of roof as well as typical projects for repairing and replacing all or part of your roof. You can also look at common roofing problems and their solutions at Pitched Roof Problems And Roof Repairs.