Skylight Installation

skylight installation, installation skylights, roof skylights, roof windows

Skylight Installation

Tips and techniques to save you a lot of trouble with your skylight installation.

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Skylight Installation:

With all of their benefits, we do have to address some concerns that you should have with roof window or skylight installation.

If you have ever herd that a product is only as good as the installation, this is especially true with skylight and roof window installations.

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I have found many times that while specifying an excellent product, if the installation isn't followed specifically according to the installation directions or if the installation contractor is not accustomed with this product, or is inexperienced, you are asking for trouble.

Your first step is to select the product with the absolutely best flashing's and installation directions in the industry. With roof windows, One of my products is Velux line of skylights, roof windows and accessories.

I have specified their product for decades without any callbacks - as long as the contractor is experienced in the installation procedure that is.

Skylight Structure

Skylight Installation - Structural Integrity

Skylight Installation - The Structure:

When your architect or designer incorporates skylights into your home roof design, make sure that the extra weight of the ice that is developed by the system is accounted for.

If your designer admits to inexperience with the product or says that they will not develop any ice (and you live in the snow belt), look around for another designer!

Skylights and roof windows will place concentrated loads on roofs that can crack plaster or in a worst case scenario, cause structural failure. So be sure they are in tune with structural design practices.

Attic Ventilation

Skylight Installation - Ventilate Your Attic

Skylight Installation - Air Ventilation:

Another extremely important issue to address is roof ventilation.

By this I mean maintaining your attic ventilation and I am not referring to the ventilation capabilities of the roof windows themselves.

Ventilation in your attic is of the utmost importance, whether you live in a temperate climate or get blasted by winter weather conditions. Attic ventilation carries away damaging moisture during the high heat and humidity times of the year and keeps your roof cold during the cold winter weather and carries away condensation that can cause wood to rot and black mold to form.

This is especially crucial when installation is in a tight structural situation, like a cathedral ceiling, where the ceiling runs parallel to the roof structure. You have to maintain the ventilation between and around the skylight structure and not allow the skylight structure to block the air path.

Roof Ventilation

Skylight Installation - Grooved Insulation

This can be rather difficult when you are building with 2x12 rafters for instance, and you place the roof structure on top of the rafter and the drywall or plaster ceiling on the bottom of the rafter.

There is practically no room left for air ventilation, let alone the skylight structure can block the flow of air as well.

One of the best methods I have found to accomplish this is to use a second layer of sheathing on top of the roof over 2"x 2" blocking. This will give you continuous ventilation over the entire surface of the roof.

Another method is to use a grooved or channeled insulation panel, as indicated in the diagram above, which accomplishes the same purpose.

Again, ask questions of your designer, architect and builder, to make sure they are very well versed with working through these conditions.

Ice Dam

Skylight Installation - How Ice Dams Form

Skylight Installation - Ice Dams:

If you live in an area that does not experience much snowfall, the skylight decision is much easier to make and you need not be nearly as concerned about ice build-up on your skylights and roof.

If however, you live in an area that receives quite a bit of snow, you are dealing with a completely different situation.

Under winter conditions, with heavy snowfall, all skylights will produce ice and ice dams. There is no way around that and we have to put systems into place to handle this known condition.

When fresh falling snow lands on the skylight glazing, it liquefies and runs down the skylight to the roof area beneath the skylight. It matters not how well insulated the glass is or the roof. This will happen.

Since the roof from the sill (or bottom) of the skylight is cold, because the attic is ventilated (or it should be ventilated) the water will freeze somewhere between the skylight sill and the edge of the roof.

Heat Tapes

Skylight Installation - The Use Of Heat Tapes

Usually what happens if you will get a solid sheet of ice from the skylight sill to the roof edge and you will get ice dams forming on the edge of the roof.

Depending on the length of the cold spell, you can get water backups beneath the roofing materials and water running down the inside of your exterior walls - not a good condition.

To prevent this from happening to you, you need to place a multi-level defense in place as follows:

You should have ice and waterdam protection membrane 24" around the perimeter of all skylights. Also place it from the edge of the roof to 24" up the roof, beyond the overhang. I.E. if your roof has a 16" over hang you should extend the membrane a total width of 40".

Also, if there is a gap between the skylight membrane and the roof edge membrane, fill in this gap with waterproofing membrane as well.

Grace Bituthane 3000

Skylight Installation - Grace Bituthane 3000 Ice and Watershield Protection

Skylight Installation - Ice and Waterdam Protection Membrane:

The best product to use for this is Grace Bituthane 3000. Hands down the best you will ever have on your roof. I used it for years and years and there is non better.

This product is placed between the roof sheathing and the underside of the roofing. Also make sure the flashing of the skylights goes OVER the waterproofing membrane, and not under it.

Install a commercial quality thermostatically controlled heat tape on the roof edge. This should be run as per the manufacturers recommendations.

I would also recommend the installation of a gutter and downspout system and the heat tape should continue in the gutter and down the downspout until it daylights out the end.

These measures will eliminate any water backup problems you may have in the snow belt areas.

Skylight Installation - What We Recommend:

After years of specifying skylights, both commercially and residentially, I have found that one of the best engineered systems on the market is made by Velux.

Velux has great products, including composite wood and aluminum units, a great variety of manufactured flashing's and installation types and a great warranty.