Double Floor Joists: What are they and why use them?

What are double floor joists?

double floor joists

Double floor joists are two joists side by side that are usually nailed or screwed together along the length.

Why would you use a double floor joist?

The main reason for doubling up floor joists is to double the strength of a single floor joist. This allows you to install a supporting post off the double floor joist to hold a second storey or a roof beam. So instead of having a post run all the way from the roof to the ground, it can stop at the double floor joist. If the post continued to the ground it could end up on top of buried sewer and drainage pipes, for example. Another benefit of this method is if you are aiming to keep the area under the deck as open as possible.

When you are building your deck, double floor joists can give you that extra strength required to support your roof or to free up some of that valuable space under your deck.

For further reading on calculations for floor joists check out some of our other articles on floor joists.

Pitfalls when estimating costs of your deck

pitfallsWhen pricing/estimating how much it will cost to build your deck, there are often a couple of points that get overlooked. The first is the quantity and the type of fixings that are required to hold your deck together and the second is the temporary construction material that’s going to be used to hold the deck together as it is being built.

When you’re pricing your deck you need to start by itemising all the individual components, such as the concrete for your footings, the posts, the bearers, the floor joists, the decking boards, etc. You also need to itemise the different fixings you’ll need to connect all the different components together; for example, the bolts that bolt the bearer to the post, or the nails that hold the bearer to the floor joist. As you go through itemising the components and the fixings, you will also need to consider what kind of temporary construction material you’ll require to hold the deck together as you’re building it. For example, when you stand your posts you need some timber to temporarily hold your posts upright while you place the other posts and bolt your bearers to them and then get your floor joists on.

When you’re pricing and estimating how much your deck is going to cost, it’s a great idea to write a list of all the different components required as well as what kind of fixings you’re going to need to secure it all together.

To help you to do this we have created the Deck Building Materials Calculations Checklist which already has all of the possible components listed. All you need to do is to make a note of which components you need and the amounts required (according to your drawings and your plans) and then in the sections provided make a note of the type and quantity of fixings that the engineer has recommended to hold your components together. Then armed with this checklist you can approach potential suppliers for all your deck building materials. By using the checklist you make it really easy for them to give you an estimate of how much it’s going to cost to build your deck. It also makes it easy to compare estimates from different suppliers.

To purchase your own copy of the Deck Building Materials Calculations Checklist you can visit the Resource Shop.

How to remove unsightly black stains from your deck.

black stain deckUnsightly black stains on a deck are caused by metal being left on a wet deck. In the photo you can see where a bolt, a bracket and even a nail have been left on the deck and they have left a faint stain behind. That big, black mess that you can see on the right-hand side of the photo has been left behind after some metal has been ground on the deck and the metal filings haven’t been cleaned off properly. Then when water gets on the deck, the metal filings and the tannin inside the decking boards have reacted to each other and created a black stain. This black stain is near impossible to clean off and when it is as bad as it is in the photo, you have no option but to sand back the deck.

To prevent this from happening to your deck, it is best to clean your deck daily making sure to remove anything metal from the deck. Even leaving other bits of timber on the deck can lead to stains which are hard to remove. Kwila timber is especially bad for this, as it is a wood that is heavy with tannins. Tannin is the sap inside timber and even though the majority of decking boards are ‘kiln-dried’, they still have a level of tannin in them.

One product you can use to clean the deck if you do have these black stains is ‘Deck Clean’, which is a mild acid. If you decide to remove your black stains by cleaning with Deck Clean, you need to scrub like you have never scrubbed before and you will have to repeat the process at least a couple of times. In some cases you will have no alternative but to sand the deck back.

For more information of on installing decking boards have a look at our “Installing Decking Boards” guide which is available from the Resource Shop.

Water leaking in behind the gutters and facia?

water leakWater leaking in behind the facia of your roof could be caused by a couple of things:

1) your roof sheets have a hole in them or your screws or nails (or equivalent) are not watertight anymore, or
2) the more common reason is where roof sheets are cut too short or they don’t overhang far enough into the gutter.

What happens in this case is that water has this capillary action which means the water travels back up the underside of the sheet just a small amount. Now when you add wind, the wind blows this water further up the underside of the sheet and if there’s not enough overhang into the gutter, the water will actually find its way over the back of the fascia and inside your ceiling or somewhere else it’s not meant to be.

This problem can be overcome by having your sheets hanging a minimum of 50mm into the gutter. If you already have your roof sheets installed you need to do one of two things:

1) replace your roof sheets with new ones, or

2) assuming that you have at least a 20mm overhang into your gutter, grab a pair of pliers or multigrips and bend down the valley of your roof sheets into the gutter.

Now this may help reduce the amount of capillary action and also reduce the effect the wind has when blowing the water back up the underside of the roof sheets. It may not work; it may work; but it’s definitely worth a shot.

For further reading, check out our other “Articles”.

What is a gum vein, and how does this affect your decking boards?

gum veinWe have all seen gum veins in decks, even though we may not have known what they were. Gum veins are the white or lighter parts of the decking board.  A gum vein is the build-up of resin or tree sap and can be identified by the vast difference in colour on the same board as shown in the photo.  At their centre gum veins are white in colour and have very few timber fibres in them. As you move towards the edges of the gum vein they become darker in colour.  The white part of the vein at the centre is very soft (you can indent the white vein with your fingernail).  As you move towards the edge of the vein, it becomes harder on account of the increasing amount of timber fibres.

So what does this mean for your decking boards?  Gum veins are a defect in the timber, a weak point.  With regards to decking, the strength of the timber is not as much of a concern when compared to a vein being in a structural timber beam, for example.  However the durability (ability to resist rot and wear and tear) of the decking becomes a concern as the gum veins are susceptible to rot.

When laying your decking boards:

  • Always cut out the white/centre part of the gum vein even if by doing so that means you need to throw away a full length of decking board.
  •  Whenever possible avoid using decking boards that have an outer edge of a gum vein in them.

By following these suggestions you will have a great looking deck that will last the distance.

For more information of on installing decking boards have a look at our “Installing Decking Boards” guide which is available from the Resource Shop.