Decks Need Strength




Two Purposes: Roof and Deck

Roofing GTA
Decks are part of the roof because they protect the area below them.  They are designed to function as a roof with extra capacity for human traffic and all the heavy things that get piled on them.  So really, the deck provides two functions: a roof and an outdoor space for people. That is why they need so much strength.

Leak from a Deck

Earlier this year we attended a leak into a resident’s living room. There were buckets on the floor catching the drips which were coming down with increasing speed from the ceiling.  It appeared that water had accumulated above the ceiling for quite a while and caused the wood above to swell.


It took time for the ceiling to actually start ripping and peeling back.  This was not a fresh leak. We opened up the ceiling and found saturated decking above that was actively leaking onto the ceiling.

Water Entry Point

We went to the roof and found the source of the leak on the deck above.  It wasn’t easy to find.  We had to pull back a layer of pavers  and disassemble the roofing system to get to the membrane. Once there we found a small tear. The concrete underneath it was soaked.  It must have gone unnoticed for months.

Why Membrane Quality Matters

There are many types of roof membranes available to builders.  Often a single-ply membranes are used to save money. Trouble is, single-ply is not durable enough handle the furniture, barbecues, planters, pavers and people that occupy the deck. Single-ply membranes, or worse, vinyl, tear or get holes.  It only takes a small hole, which is difficult to notice without testing, to cause a terrible roof leak.

We recently investigated leaks from several units in the same building. As you can see from this photo, a dropped key was enough to puncture the “protective” membrane and allow water ingress to damage the building structure and unit contents.  Sadly that was not the only puncture on this deck.

Residents want to enjoy their deck as much as possible.  Whether entertaining, lounging in the sun or gardening: People  want to get as much use out of the deck as possible and they place heavy things on it.  Barbecues, planters and furniture that is built to withstand windy days and harsh weather: all heavy items that get lots of use.


Drainage, sloping and waterproofing are vitally important to a deck because it also functions as a roof.  As we always say:  regular roof maintenance is the best way to keep all parts of the roof in the best shape possible including the decks.

Leak Investigations

When a tenant spots an obvious leak you have an emergency on your hands.  That roof leak could be something that built up over time and has finally come through, or it could be something sudden that had a clear cause.  Whatever the situation is, you know you need a technician in as soon as possible to do a roof leak investigation.

So what really happens when a technician shows up?

We perform an investigation by finding the leak and taking steps to trace it back to the source.  It depends on where it is, sometimes we have to look into attics or rafters, around windows and soffits. Lights, skylights and vents are also places our technicians look for water ingress.

roof leak repair


Here a tenant spotted a leak and put down a bucket with some tarp.  We were alerted.

Leak Area on Deck

We started the leak investigation by looking at the deck directly above the leak.

removed bricks above leak

We lifted the bricks and insulation and stacked them to the side so we could inspect the membrane underneath.

Plugged drain repair leak

We discovered a plugged drain and some ponding water.

Disposed of debris causing plug

The drain was plugged with debris so we removed that and relieved the ponding water.

roof membrane hole

We discovered a small penetration in the membrane.

deterioration of roof membrane

While there we found the membrane was deteriorating.

Applied water cut off mastic

We cleaned and prepared the membrane and  applied water-cut-off mastic to temporarily seal penetrations and deteriorated membrane found on the deck.

roof membrane failure

Upon further investigation we discovered the corner membrane had failed.

Used water-cut-off mastic

We applied water-cut-off mastic to temporarily seal the failed membrane in the corner of the deck.

SBS base shee to protect

We installed an SBS base sheet as an additional protective layer.

In this leak investigation there were a few reasons for the leak.  There was a small hole in the roof membrane and the drain was plugged.  The plugged drain caused water to pool, which found it’s way to that hole.  The other issues we discovered while there would have led to more leaks.  These temporary repairs need to be followed up with permanent repairs.

Decks Need Extra Special Care

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