How to Slate a Roof
Slate is a very common material used to cover a roof. However, it requires a specific process in order to be laid or repaired. If it is properly maintained, then it can have a very neat look alongside protecting your roof from the weather.
If you are looking to lay a slate roof, or replace one or more broken slates, this post has been written to help you understand the steps that need following, in order to correctly install roofing slates.
Safety – Caution When Handling
All roof coverings should be treated with care. You need to ensure that you take the necessary precaution in order to protect the materials when laying slates on a new roof or replacing a slate on an old roof.
When you are working on a roof, you must ensure that there is sufficient protection around the roof, such as scaffolding. You should keep a ladder securely fixed in place along one side of the roof, and it is best to have someone holding it at the bottom, for added safety. As with any job you should be wearing the correct PPE including all clothing, footwear, gloves and hard-hats.
Underlay – Preparation
After the rafters have been fixed, you need to cover and fix the underlay. Starting from one side of the roof, making sure the underlay is set square against the verge, fix the end of the underlay in place at the furthest rafter. Now roll out the underlay across the roof, and fix the other end in place, leaving slight slack in between the rafters.
You can fix the underlay along the middle if you wish, although this is not mandatory as the battens that will be fixed in later will secure the underlay in place. This is repeated until a section of the roof is completely covered.
Battens – Making a Start
Now that the underlay is fixed in place, you need to calculate where the initial battens will be placed. You can do this by using two full-sized slates and an under eaves slate. Place a full-size slate at the lowest edge, keeping in mind the required overhang into the guttering, generally no less than 50mm.
The calculation is: The Lap + The Gauge of The Batten + 50mm. Making sure you allow for 50mm into the guttering, work away from the edge and fix your batten underneath the head of the eaves slate. The next batten fixed will hold the first row of the eaves course, line up the tails of the batten and locate the holes in the first full-size slate, then fix in place.
The manufacturer of the slate you are using will more than likely establish the amount of slate lap needed to adjust for. The ‘lap’, is the amount of overlap between the holes for the nails in a full-size slate and the bottom edge of the slate above it. Now you can batten the rest of the roof using the gauge outlined, or you can calculate it by: Length of slate – the lap divided by two, this will leave you with your gauge for the batten, centre to centre.
Slating – Setting Out & Laying Slates
Snap a chalk line from the eaves to the ridge at the width of each slate plus a 5mm joint between each slate for expansion.
Now fix the under eaves course (smaller slates). They should be laid first, starting with a one and a half sized slate, in order to create a staggered pattern. Ensure you maintain a 5mm gap between each slate to allow for expansion.
The first full-size slate should be laid and have the tail aligned with the under eaves course with at least two 35 x 3.35mm copper nails.
Continue working toward the top as the slates are laid, moving in a diagonal direction from the bottom of one side to the top of the other. This will severely reduce the number of slates that are stood on during the laying process, lowering the risk of breaking any slates. There should also be a minimum of two nails per slate, you may use more but be careful not to use too many.
The top row of slates requires the use of special top slates that are cut down in size. The batten used to fix these slates needs to be a minimum of 5mm thicker than the battens used throughout, this is to ensure that the slates are fixed securely.
Slating – Replacing a Broken Slate
Slates are more than likely fixed in place with copper nails, so before you can replace any slates, the nails in the broken slates need to be removed. To do this you should use a tool called a Slate Ripper, alongside this you will need a Hammer, a pair of Snips (Tin Snips preferred) and a Slate Trimmer to cut down the new slate being placed if needed, we will call the new slate, Slate B.
Put the hooked end of the Slate Ripper under Slate A (the slate that needs replacing), and locate the nail in the hook. Now use a Hammer to hit the handle of the ripper, forcing the nail out of the slate and move everything away from the slate. Repeat this process for any more nails in the slates that need to be removed.
After this, you may be able to slide Slate A down and out of place. Apply light pressure to the top of the slate and keep the Slate Ripper underneath to help get it out. Slate B needs to be a perfect fit for the space left, use the Slate Trimmer if necessary to get it the right size.
If more than one slate has been replaced, the new slates should be able to be fixed back to the battens with nails. However, the final slate will be slightly different. The final slate will need to be fixed with a piece of lead long enough to be secured to the batten, and a little extra to wrap around the slate.
Fix it in place using nails, and the put the slate ripper over the existing slates in order to slide Slate B into place. The lead along the bottom of the slate should be slightly visible. Ensure that Slate B is square and level with the rest of the slates surrounding it, and that is pushed all the way up to the batten underneath.
Now fold the lead over the bottom of Slate B to create a hook, this is designed to keep the slate in place, and use the snips to cut off any excess.
The processes of laying and maintaining slate roofs are not complex. As long as you have the correct tools for the job and take time to carefully and methodically plan and prepare for the work, you will be able to create an aesthetically pleasing and versatile roof.