How to slate a Roof
June 15, 2024Flat roof replacement
June 15, 2024
HOW TO TILE A ROOF
Roof tiles are typically fired clay or coloured concrete, and come in a variety of shapes and sizes. This article deals with the key skill of tiling any roof, which is setting it out. If you meant how to slate a roof click the link provided, alternatively if you want to know how to replace all types of roof tile, including hanging tiles, see the link at the bottom of the page.
HOW TO CALCULATE HOW MANY ROOF TILES YOU NEED
My technique on domestic properties has always been simple, I make an educated guess. By that I mean for estimation purposes I can stand looking at the face or faces of a roof and write down the Width and Height of each individual face of the roof on a piece of paper. Then when you add them up you are going to be left with a square metreage or square footage figure. You can also measure the width from ground level, I find it’s quite easy to work in metres from my minds eye, but then again I’ve done a lot of it. Alternatively get a nice strong tape measure, get up some ladders and measure it.
Alernativley ‘Google’ a roof tile calculator like this one Calculating Roof Tiles
Now you have a square metre or square foot figure, ring up your local roofing supplies merchant and they will work out how many tiles you require for your roof.
ROOFING LATHS ROOFING BATTENS
Roof lath or roofing battens, two different names for the same thing. Strips of tanalised timber often pressure treated with a wood preservative of some description. These are nailed into the roofing joists or roof trusses beneath and provide support for the roof tiles or slates, fixings can then be made into the roofing lath or batten if required.
The most common sizes of roofing lath are…
- 18mm x 36mm (3/4” x 11/2 “) Commonly called slating lath or slating batten.
- 25mm x 38mm (1″ x 11/2 “) Commonly called tiling lath or tiling batten, often used on rafter spans of 450mm or less.
- 25 or 30mm x 50mm (1 – 11/4 ” x 2″) Mostly used in modern tiled roofs, often used on rafter spans of 600mm or less.
Roofing batten – Common sizes of tile lath, slate lath or tile batten.
HOW TO SPACE ROOF TILES AND SPACE ROOF BATTENS OR LATHS
An awful lot of people including Builders and Roofers get the layout of a new roof wrong right from the start, subsequently they end up with a leaking roof, or one that just looks awful. I’m going to show you the right way to space the tiles and battens so your new roof project is correct from the outset.
The most common mistake made is that the tiling takes place at the bottom of the roof from the scaffold at gutter height, no thought is then given to whether the tiles will be correctly spaced by the time you get to the top of the roof. When laying roof tiles it’s important just to spend a little time planning tile spacings (gauge) first, as it pays real dividends later
Badly tiled roof with the wrong tile spacing – This is a good example of what goes wrong with tile spacing and batten spacing when it’s not thought through.
The bottom tiles are stretched, the middle is passable with chaos at the top.
Here’s a good example of a nicely tiled roof, let see how it was done…
New concrete tiled roof – This is a nice simple roof, here I’m going to deconstruct it to show you how it was achieved.
Once the old roof has been stripped all the way to the bottom, the rafters or roof trusses will be fully exposed. Make sure the rafters are clear of any stray nails or nasty splinters, so they are ready to take the under tiler’s felt or breathable roofing membrane and not rip or puncture it. One full width of 1F roofing felt has been fitted in the picture below and tacked in place using 25mm (1 inch) galvanised clout nails.
Find out more at HDM Roofing Services
HOW TO LAY ROOFING FELT OR ROOFING MEMBRANE
Start on one edge of the roof and fix with two or three nails then roll out the roofing membrane or felt keeping it taught but with a very slight hint of sag, this will ensure any water that does end up on the felt will run between the rafters and end up in the gutter. Make sure about 30 to 40mm of felt hangs over the fascia and into the gutter, too much felt hanging inside the gutter will impair water flow and encourage dirt build up inside the guttering. On a traditional construction, if there is a cavity wall, make sure you bridge the gap over any cavity with the 1F or membrane.
How to start tiling a roof – New 1F under slaters or under tile felt stretched across clean roof rafters.
Secure in place with galvanised clout nails, don’t overstretch or go crazy with the nails. The roofing battens will also hold the felt in place when fixed.
FITTING UNDER TILER’S FELT OR INSTALLING MEMBRANE…
- Joining felt or membrane – Avoid joins if possible, otherwise overlap any vertical joins by 100mm (4″) onto a rafter or truss
- Overlapping felt or membrane – When laying the next layer above the pervious overlap, make sure the cover is about 150mm (6″)
- On a Hip – Make sure the felt or membranes overlap goes around onto the next face of the roof about 150mm (6″)
- On an upstand – Where the roof joins or abuts a wall turn the felt or membrane up the face of the wall for 50mm (2″)
- On the verge – Cut the felt or membrane at the outside edge of the last joist
- At the ridge board or apex – Overlap 150mm (6″) over the top of the roof onto the other elevation
HOW TO SPACE ROOFING LATH OR BATTENS
Next we need to work out the spacing of the tiles and the spacing of the battens up the roof, this is commonly called the ‘Gauge’ , often this will be specified by the tile manufacturer or the roof tile supplier, but to work it out properly you will have to do the math yourself as every roof is going to be a different size or shape. Tiling to top ridge board or apex of the roof and achieving nice even tile gaps is quite simple as long as you think it through a little first.
HOW TO SPACE A TILED ROOF
Firstly get two of your roof tiles, and either two full battens or two offcuts of batten and place them onto the roof one above the other. Next place your two tiles, one on top of the other loose onto the battens without anything being fixed. Make sure the tile lugs are seated snuggly onto the top edges of the battens.
Batten spacing – Roofing battens or roofing laths placed loosely onto the roof with the tiles seated on top of each other. Next the roofing battens are not fixed at this point to allow adjustments.
Now using a tape measure we can work out the basics for your new roof.
- Tile overhang – How much tile should be in the gutter
- Tile lap – Tile lap or how much to overlap one tile above another
- Tile gauge – Tile spacing or spacing of the battens
HOW MUCH ROOF TILE OVERHANG IN THE GUTTERING
The simple answer is not really beyond half way, if there’s too much tile in the gutter the rain water can overshoot the gutter in heavy rain, and make the guttering hard to clean. If the tiles are too short then rainwater can dribble down behind the gutter and be blown against the fascia boards. I think somewhere around 50mm (2″) is about right in most situations, (see Figure 1 in the picture below). Set the bottom tile gutter overhang now.
HOW MUCH ROOF TILE OVERLAP
This is normally specified with the tile manufacturer and it’s advisable to check how much they say a roof tile should overlap, normally on a smooth faced tile the overlap is 75mm (3″) and on granular or sandfaced tiles its 100mm (4″) however if the roof is shallow pitched, is facing a windy direction or will be prone to moss build up, it may be a good idea to increase the lap by another 25mm or (1″). (Tile overlap seen in Figure 2 below).
SPACING ROOF TILES AND BATTENS
When setting the necessary tile overlaps with the tape measure, the Ideal tile spacing or gauge is the distance between the top of the first batten and the top of the second as in Figure 3. Here the tiles are overlapped 75mm (3″).
How to space roof tiles – Set tile overhang into guttering – Set recommended tile overlap – Reveal the ideal batten spacing (gauge).
HOW TO WORK OUT ROOF BATTEN GAUGE
The initial gauge for this roof happened to be 131/4inches or 33.5cm measured from the top of one batten to the top of the next. What we need to do next is fix the battens in place with something like a 50 to 60mm galvanised nail (2″ – 21/2“) using the edge of the fascia as the reference point for the bottom batten, and the top of the first batten for the second batten. Nail size obviously depends on the size of the lath or batten you are using, but it’s recommended that the nails penetrate through the batten and a minimum of 40mm (11/2“) into the rafters underneath.
MEASURE THE REMAINING ROOF AND HOW TO CALCULATE THE BATTENS
Now we need to measure the remaining roof from the top of the second batten to within about 30mm or11/4” of the apex or ridge board. This is so we can work out how many battens we require, and work out any changes we need to make to our initial gauge figure so that the batten spacings are equal all the way to the top of the roof.
Batten spacing – Measure the distance between the top of the second batten and 30mm short of the top of the roof. This will allow the tile lugs to fit nicely into this gap without danger of pinching or breaking them.
HOW TO WORK OUT TILE AND BATTEN SPACING IN METRIC
In this case the remaining roof measured 458.5 cm to the finishing position i.e. the top of the last batten. Having figured out earlier that 33.5 cm was the ideal batten spacing we simply divide the 458.5 by 33.5 to get the figure of 13.68 on the calculator. So 13.68 is the amount of additional battens required.
Obviously 13.68 rows of batten isn’t a workable figure so we round it up to 14, we now know we will need an additional 14 rows of batten to complete the roof.
Now we need to know the spacing measurement for 14 rows to fit in our gap of 458.5cm, so we divide it by 14 and end up with 32.75, this means the new gauge to ensure correct spacing of the battens is 32.75 cm.
If you want to double check this figure multiply 32.75 by 14 and you get 458.5 cm
MAKE YOURSELF A BATTEN SPACER
Now you have your desired batten gauge, consider making a roof batten spacer out of an old off-cut of batten. When cut to the desired gauge it will allow quick and easy placement and fixing of the tiling batten, simply by placing the spacer upright on top of your last fixed batten.
Batten spacer – Placed onto a rafter beneath the sarking, every subsequent batten will be accurate and easier than repeated measurement. Just remember to re-check the distances so that all remains parallel a few courses before the top, to make any final corrections if necessary.
FIXING THE BATTENS TO THE ROOF
Continue fixing the battens one above another, once you have completed one horizontal run of batten, felt or membrane, you can stand or sit on the battens you have just fitted where they intersect the rafters. Make sure the quality of your batten timber is good and there are no dangerous knots or splits as this can be a health and safety issue. To lay on the next run of membrane or felt, start fitting more batten to the gauge you have worked out, continue this sequence all the way to the top of the roof and overlap the felt or membrane at the apex as 150mm or 6″.
Fully battened roof ready for tiling – Where the roof overhangs the walls if you’re using the traditional mortar bedded verge or gable end you will need to slacken off the battens to slip ‘fibre cement board under cloak’ underneath ready to take the mortar later.
WANT TO KNOW MORE?
Another great source of roofing related knowledge I have stumbled across is a great little book called Roof Tiling and Slating, and having read it I can definitely recommend it.
It also lists tools, materials, roof shapes and considerations for planning your job. Slates, both natural and manmade, as well as concrete interlocking and plain tiles. There’s also information on valleys, ridges, verges and other details I have yet to cover in videos or on the website so far.
FINALLY… WORKING OUT TILE SPACING IN IMPERIAL FEET AND INCHES
In this case the remaining roof measured 1771/2” to the finish position, i.e. the top of the last batten. Having figured out earlier that 131/4” was the ideal batten spacing we simply divide the 1771/2 by 131/4 to get the figure of 13.39 on the calculator.
Obviously 13.39 rows of batten isn’t a workable figure so we round it up to 14 rows, so now we know we will need an additional 14 rows of batten to complete the roof.
Now we need to know the spacing measurement for 14 rows to fit in our gap of 1771/2 ” so we divide it by 14 and end up with 12.67 on the calculator, again this is no good if you’re working in feet and inches so we round it up to 12.75 or 123/4” (.75 being three quarters)
If you want to double check this figure multiply 12.75 by 14 and you get 178.5, as you can see this is only 1″ out of the 177.5 required so adjustment to batten spacing can easily be made for this on the last two rows without any visual or structural impact.
