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Expert Advice: how to install a skylight

All you need to know about skylight installation for both period and new-build properties

scenario architecture white room with skylight
Matt Clayton

Installing skylights into a new build is infinitely easier than into anything old.

1 It’s all very well choosing a window that will fit between the joists to minimise chopping, but when those joists are 100 years old and revealed to be extraordinarily wonky, you realise you need to measure the real dimensions, not the theoretically perfect ones as guessed externally.

2 You really need to know what your roof is made of before you start works.

3 Check the pitch of your roof. 15 degrees is the minimum for decent rain run-off. Velux has a roof pitch indicator app that you can download for free, so it’s easy to do. That said, you need to check again once the roof is stripped.

scenario architecture skylight room
Wraparound views: When updating this 1990s property with a roof extension, Scenario Architecture filled their new top-floor space with light. In particular, the owners wanted a view of the garden roof terrace. The solution? Lower the roof terrace and glaze it, creating a long ceiling-height window above the main living space.
Matt Clayton

4 Don’t forget to factor in the cost of ‘making good’ after works are completed. Not all roofers expect to do this for you, so it won’t necessarily be included in their quote, unless you ask. I ended up needing to get the whole inside of the extension re-boarded,re-plastered and re-wired.

5 To cut a long story short, strip and show what you are working with before you buy windows if your property is old with a roof made of anything other than nice straightforward joists and tiles.

roof with skylights
Jack Woolley
room with skylights
Jack Woolley

This property (above) in north London was designed by architect Jack Woolley
to channel as much light as possible into its below-ground levels. Clever skylights and windows ensure that the home, which is packed into a tight urban spot, never feels dark or cramped.


If your roof is new, or newish, then installing Velux windows will be a breeze. Almost any builder will have put them in before, plus the company has an army of on-hand installation experts you can telephone, or call out, if there are any complications. Skylights come internally finished in white painted wood, white polyurethane or pine, and there are options for use in conservation areas. There are lots of standard sizes on offer, plus custom options, blinds and shutters. But you still need to do your research before you order. Here’s my starter list

1 Check the pitch of your roof to determine exactly which types of skylights you’re able to specify. Under 15 degrees qualifies as flat, and there are fewer models available for this.Over 15 degrees, you’ll have lots more options to choose from.

2 Be sure what roof finish you’re going for – tiles, asphalt and slates each require different flashing solutions (the way the skylight is wrapped to ensure no water ingress around the edges).Each finish has significant pros and cons. Consider the weight of classic tiles (can existing joists take it?), fibreglass stinks when being installed, asphalt is easy but ugly, and some slates can’t be used on low pitches.

brick house rear elevation with skylights
Aptly named ‘The Lantern’, this home in south-west London, designed by architecture firm Fraher & Findlay, is characterised by its manipulation of light. After obtaining planning permission for a side extension on this listed building, the owners and architects decided to separate the original property from the new brick-clad addition using a giant vertical window that extends elegantly over the roof.
Fraher

3 Check with both your builder and Velux the distance apart you wish to fit a run of skylights. There are set dimensions that are preferable – usually ten centimetres minimum – which means most installations should fit neatly either side of existing joists, assuming they’re parallel.

4 Will you be able to reach your skylights? If not, consider the Velux ‘Integra’ solar powered remote control-operated options. Or remember to buy a pole.

5 Look at loads of case studies (see buildinginspiration.co.uk) to fully understand all of the options before you buy. You only want to do this once. Velux Skylights, from £264 velux.com

This article appeared in ELLE Decoration November 2016

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