Decks Need Extra Special Care

July 17, 2015 Laura MacCormac

Sometimes we forget that decks are part of the roofing system. It’s important they get the extra special care that decks need. To be clear, decks and balconies have different definitions.  A deck is a surface you can walk on, that is exposed to the outdoors and is over an enclosed space below.  A balcony has a similar definition, but does not cover an enclosed space.

As decks are part of the roofing systems, all roofing components are part of it: gutters, drains, guardrails etc.  Other considerations like extra weight on a deck, must also be taken into consideration.

Weight on the deck

The main component of every roofing system is the membrane.  However on decks, the membrane is typically covered with a walking surface like tile, pavers, wood,  concrete, etc.

There’s more foot traffic on a deck than a typical roof; Why have a deck if you’re not going to use it.  People place planters, bikes, furniture, barbeques, and other heavy things on the deck for their use. A deck needs to be able to handle all this weight, and protect what’s under it at the same time.

Plantars on a deck



Planters are heavy and when they’re filled with soil they can weigh hundreds of pounds!  Soil weighs around 100 pounds / cubic foot, more or less depending on moisture content.  Add to that the weight of the planter itself and you’ve got the weight of at least two adults right there.

People put a lot of weight on a deck.


Deck floors are usually covered with wood, tile or pavers, which are square slabs of concrete.  These weigh in at 70 lbs each.  This gives a deck with 50 pavers a load of 3500 pounds!

Add to that the barbeque, the furniture and the people and you’ve got a lot of weight on the deck.

Special Care with Repairs

When we do repairs on decks we are extra careful about how we go about it.  Fire safety is a big priority on decks and we often use alternatives to torching, because it’s so close to a work or living space.

Flamable items in living spaces mean it's best not to torch them.


Liquid Membrane Repairs

There are alternatives to torching on a base and cap sheet.  One method is to use a liquid waterproofing membrane.  There are many types of liquid membranes that can be used. Here’s an example of how we use one type of liquid membrane, aquabloc, to repair a deck.

Gravel and mesh removed

Repair area cleaned

Applied aqua bloc

aqua bloc over mesh

june 15, 2015 122330 pm edt-resized-500


flam applied over aqua bloc

june 15, 2015 122920 pm edt-resized-500

laid mesh

gravel redistributed

Different  types of liquid membrane can be used for different types of decks.

In this example, we covered deteriorated concrete  with a primer and a coat of alsan 525  liquid membrane.  We spread the primer and first layer of alsan 525, allowed it to dry for a day. We returned the next day and put down a second layer , this time primer and alsan 535, complete with an aggregate coating for surface grip ability.

Applied primer

may 13, 2015 45450 pm edt-resized-500

wet paint do not enter


We let the deck dry for a day.

apply alsan 535


Once dry, we apply a second layer of primer and a coat of Alsan 535.

The Thing About Vinyl

If vinyl is used as a membrane, it is typically done on a balcony, not a deck.  this is because it is not as strong as a two-ply system.  Vinyl is a poor quality membrane that easily tears, letting water in underneath which leads to mold and rot.

 Drainage Cannot Be Forgotten on a Deck

Decks are part of the roofing system and are exposed all the elements, like snow and rain.  However, because of their structure, they can hold water like a tub, which is why drainage is so important.

drain in the deck

Sometimes the drain is hiding, but it should be there.

drain under pavers


Here’s an example of a deck with several holes that lead to a drain.  Pretty clever.


extra drain holes



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