How to install a skylight by yourself

2006-11-11 15:34:06

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Skylights provide an economical and very practical way of lightening up a dull or dark room or passageway with the added benefit of saving on energy cost. In this MitrePlan we look at two types, the rectangular style which requires a light shaft to be constructed to suit the roof and ceiling conditions and the circular style commonly known as a 'domelight' which has a pre fabricated shaft as a part of the kit (Fig. 1). And they do both differ, the 'domelight' is easier to install but does not throw as much light into the room, the rectangular skylight will require some extra work by way of structural alteration and fitting the light shaft but gives more added light per unit. Of course the effect of the 'domelight' can be increased by strategically placing more than one into a room, and with their simple circular diffuser this may just be the effect you are after.

Before you start

Look at the room or area that you want to add light to and with the available natural light from an existing window source decide the skylight location which will give the best lighting benefit. Available external light will vary depending upon the compass orientation of your roof plane (Fig. 2). A skylight fixed to a south facing roof plane is going to have very limited effect, one fitted to a north facing plane will have best lighting effect for most of the day, one on the east best in the morning, and a skylight on the west will be of benefit in the afternoon.

Skylights are also available with fixed ventilation incorporated around the dome. You will need to specify whether you want ventilated or sealed skylight at the time of ordering your skylight at your Mitre 10 store.

Now that the preferred location is identified inspect the space between the ceiling and roof for obvious obstructions such as electrical, plumbing, air conditioning ducts etc. If there are any of these are in the way and you are unable to re-position the skylight location then call in the appropriate trade experts before proceeding with the job.

Pre fabricated skylight installation

Domelite and room diffuser location need to be positioned in as direct a line as possible so the shaft is free of any excessive bends.

Locate on the roof where the skylight is to be installed and remove six tiles (Fig. 3). Check once more that the way for the shaft to the ceiling is clear of obstructions. Place the flashing tray on the roof battens in the fianl location and secure it to the roof battens with the provided fixing method. Next mark the location of the diffuser between ceiling joists on the ceiling and cut out the plaster to the required size.

From in the room fix the diffuser into position. Now get back into the ceiling space and run the duct from the diffuser up to the skylight location. Mark the length of duct needed and remove and cut any excess off to the correct length. Replace the duct onto the diffuser and fit while fitting the duct to the skylight collar. Complete any required fitting of the domelight to the flashing tray, and finally check that all components are securely fixed and held down in accordance with the manufacturers recommendations.

Step 1: set out

Once the location and size of the ceiling opening has been decided, mark the centre of the proposed opening. Drive a 50mm nail into the ceiling at this point and inspect the location in the ceiling space to ensure that the way is clear of all obstructions. You may need to adjust the location to suit existing conditions.

From the centre nail mark locate where the actual skylight will fit on the roof. Remove enough tiles so that the whole skylight and flashing can lay on the roof battens (Fig. 3).

Step 2: framework

The skylight will have a top and bottom edge to the flashing, the bottom edge is generally of a malleable substance and the top has a rigid flashing tray. Locate the skylight so that one side of the shaft will sit alongside a rafter and the top of the metal frame is just below the nose of a full tile (Fig. 4).

If a rafter runs through the centre of the skylight mark the inside edge of top and bottom of the flashing tray, measure an extra 35mm on the top and bottom (so cut section of rafter will be 70mm total oversize). Using the spirit level mark a plumb line down from these marks and cut the rafter section out. Measure the distance between the rafters and cut trimming pieces (Fig. 5), nail securely with 2x75mm nails per join. This ensures the roof structure remains intact. If you are unsure check with a qualified tradesperson for advice. Your local Mitre 10 store can help you fing the right person for the right advice.

Next cut off the roof battens that run across opened area.

Step 3: the skylight

Position the skylight on the framing and screw the flashing tray down to the roof battens. Seal the screws with a generous amount of silicone, and replace the roof tiles on top of the flashing tray and roof battens. Some tiles may need cutting to give full lap onto the flashing tray. Press the bottom flashing to mould it to the profile of the roof tiles. Now the roof is sealed and weatherproof. Remove all debris and clean down roof and gutters.

Step 4: the shaft

The dimension of the diffuser in the room is dependant on the angle of the shaft from the skylight (Fig. 6). Careful use of a spirit level and ruler is needed here to determine the dimension of the shaft. From inside the ceiling space transfer the shaft dimensions down to the ceiling around the centre nail location done earlier (Step 1).

Cut the plaster ceiling to these marks, then mark any ceiling joist that is in the way, add 35mm to each side of the opening, cut the joist and then measure the distance between the joists and cut trimming pieces (Fig. 5), nail securely with 2x75mm nails per join.

Measure the width of the side panels to the shaft at the top and the bottom, also measure the length. At this point use the length measurement as a reference point at which to mark top and bottom widths. Cut the sheet to width. Position the sheet in the shaft and mark the top cut to suit the angle of the skylight (Fig.7), remove the sheet and cut the top to this dimension.

Replace the sheet into the shaft in position against the underside of the skylight and mark the overall length of the shaft side to the underside of the ceiling lining with a pencil. Repeat this measureing and cutting procedure for the opposite shaft side. Remove the sheet and cut to length. Now place both shaft sides into the ceiling space and securely fix with 40mm screws to the framework at the top and bottom.

The remaining two sides are measured and cut to fit in between the two fitted shaft sheets, these should be parallel and have two square ends so pre-fitting will not be necessary. Place the sides in between the fitted sheets and fix to the framework at the top and the bottom with 40mm screws and also along the edges at 300mm spacings.

Step 5: the diffuser

The base of the skylight at the ceiling is finished off with 70mm x I6mm architrave, which is placed overhanging into the shaft by 25mm - this is for the perspex to sit on and with mitre cut corner joints. Fix the architrave to the framework with 50mm bullet head nails.

Measure at the base in between the shaft walls for the perspex diffuser and deduct I0mm off the measurement. Order the perspex in your desired finish, you have a wide range of choices including opaque, prismatic, clear etc., or you could even use some decorative style leadlight glazing - refer to MitrePlan 57 - Make a leadlight panel - for more information.

Now all that is left is to paint the architraves, and while your at it you may even want to freshen up the room by repainting the walls and ceiling to maximize the new feeling created by the skylight. Of course with assistance from Mitre 10.

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