Preparing a new roof deck – flashings


There are many different parts of a roof and flashings are what protects the roof at all its vulnerable points such as along the eaves, in the valleys and at the edges of the roof chimneys, roof vents and skylights. It is basically there to protect the roof from water leaks at the joints, protecting the sheathing underneath. Flashings are normally made out of galvanised and rust-resistant sheet metal. When you are doing work on your roof, you might not have to change the flashings as long they are in a good condition. Check it over and reseal any flashing joints, if need be, with a bit of plastic cement. Remember to use protective gloves if you are working with metal as the sharp edges can give you very bad cuts.


New valley flashings

If you have checked over the exiting flashings and come to the conclusion that it will have to be replaced, this is how you install new valley flashings. It is important that the flashings in the valleys are particularly sturdy as they transport more water to the gutters than any other parts of the roof planes. Despite most valley flashings being made of galvanised steel, you can use mineral surface rolls for the valleys on asphalt roofs. There are different finishes such as open and woven valleys. The first are where shingles, or tiles for that matter, are cut in order to expose the valley. The latter one is where asphalt shingles overlap and covers the valley.


Installing new valley flashings

If you are roofing over a new or a completely stripped deck, use galvanised metal of 28-gauge for sloping roofs. This is regardless of whatever roofing material you are planning to use. You do not have to make your own valleys, unless you want to, as you can buy them from most roofing suppliers. Just make sure that they match the slope of your roof. If you purchase them, you will notice that they often come with splash guard at the centre and the outer edges will have be crimped in order to direct any water to the centre. The metal should reach about 8 – 11 inches up along each side of the valley. It you are planning to roof over asphalt shingles, a roll roofing of 36 inches wide can be used. Just make sure to match it to the new shingles – this is most important at the valleys.

Roofing decks for tile roofs

The parts of the roofing deck

When it comes to tile roofs, the actual roofing deck has three parts. The first part is the solid sheathing, the second part is the underlayment and the third is the furring strips that are often used if the tiles are concrete. Furring strips help some tiles with anchor lugs to stay in place and depending on the slope of the roof, they can be nailed to the strips. This is also the case if you live in an area with strong winds. Tiles with no anchor lugs, are nailed directly to the roof and on top of the felts but they can also be fastened, suing a wire. This is not as common though. I would always recommend checking what the building code for your area states as this can differ depending on where you live and what whether you are likely to be exposed to.


Furring strips

Sometimes tile roofs will need furring strips and these needs to be installed at even intervals. The intervals need to be equal to the actual expose of the tile. This basically means to measure it between the upper edges of any successive strip. If you are using flat tiles, a furring strip has to be nailed flush with the eave. If you are using curved tiles, the so called ‘birdstop’ flashing should be nailed at the eave. Lay a sample tile along the eave by each rake. The recommended overhang is normally about 1 and ¼ inches if your roof has gutters and 2-3 inches if your roof has no gutters. Remember to make a mark where the tile lugs will grip the upper furring strip edge at the rakes and snap a chalk line in between. The next sections of furring strips should be 4 foot long and be installed with their upper edges against the chalk line you just made and then nail them to the roof where they cross a rafter. Allow about half an inch of spacing between abutting strips so that any rain water can run off. A furring strip should be installed at the roof ridge with the upper edge about one inch from the edge. Measure the length between the upper edges of both furring strips and decide it by recommended tile exposure. I would do this a couple of times just to make sure the measurements are correct. Where the roof divide into whole multiples of the exposure, mark the exposures along each rake. Always start at the top edge nearest the eave, snapping horizontal chalk lines between the rakes. Now you can install the furring strips with their upper edges against the chalk lines. If your roof does not divide into whole multiples of the exposure, you will have to decrease the exposure slightly for all the courses. Remember to never ever increase the exposure – always decrease. Good luck!



Hi and welcome to my blog. If you are interested in DIY and would like to learn new skills that you can use around your home, then this is the blog for you. One of my biggest interests is renovating my old house and fixing things that are broken. In this blog I am hoping to cover some of the projects that I am currently working on and projects that I have already completed. I hope you will enjoy it.