Deck bearer to post fastener | Termite repellent membrane

[vinzzze]

Hi All,

My apologies for the length of this post and for asking two questions in a single post. My apologies also for my terminologies for being a newbie DIYer.

I would like to seek for the community's expert advice regarding post to bearer fasteners and termite repellent membrane material.

According to my draftsman drawing, my bearer must be fixed on top of the post. The bearers are double 90 x 45 H3 F7, and the post is 100 x 100 F7 H4. The joists are single 90 x 45 H3 F7. (I am from Victoria if that matters)

This is for a 6.7m x 3.3 m low level deck with an estimate of 450-600mm deck height.

The joists are connected to a 190 x 45 ledger which is screw mounted to a brickwall.

My question is for the bearer to post (stump) connection. If I use a T or L plate to fix the bearer to post, I can only fix the bearer on one side. The plate won’t flush on the other side because of the 10mm gap (90mm sitting on 100 mm). If I use a nail plate, I will have to bend it a bit for the 10mm gap. My option is to just mount the L or T plate on one side and bolt it through and through on the laminated bearer or ask the draftman if 90 x 90 is sufficient so the bearer is flush on the post, and I can use plates on both sides.

Do you have any recommendation on how to better fasten the bearer?

My other question is regarding the ledger. The draftsman noted that the ledger (waling plate) must have either a 25mm gap or apply a termite repellent membrane. May I ask for your expert advice where can I get this material? I found termite barriers in my search. Which I find it hard to source for minimal amount and seems to be installed by certified installers only. Does anyone have an idea regarding this requirement? Or perhaps an alternative material. I told my draftman that the ledger is already H3, why do I still need a termite membrane?  

[EricL]

Hello @vinzzze

Welcome to the Bunnings Workshop community. It's fabulous to have you join us and thank you for sharing your questions about your deck project.

I suggest asking your local council if they have a list of approved products for termite barriers between the house and deck ledger. That should make searching for an approved product a little easier. However, if the council requires the job to be signed off by a certified termite barrier installer, I'm afraid you'll have to let the professionals do this one.

However, in regards to the 25mm spacer between the house and the ledger, it is definitely achievable. There are some specialized spacers you can purchase online, but I suggest using galvanized washers. Galvanized washers are the traditional spacers used in creating gaps between ledgers and the house wall. 

Again it is vital to check with the council on approved methods of installation of the mounting bolts and washers. Your draftsman would have indicated on the plans the location of the mounting bolts and what size were to be used. 

As for the bearers on a larger post, the traditional method of mounting a smaller bearer on a larger post is to do a scarf cut on both sides of the post. This will allow you to put a nail plate at an angle and secure the bearer to the post. Please ask your draftsman if this method is permitted or you can ask your local council.

And in regards to the question about the termite barrier, Australian standards require that a barrier must be installed when adding an extension or renovating a home.

Let me call on our experienced members @Adam_W, @TedBear, @ProjectPete and my colleague @MitchellMc for their recommendations regarding your decking questions.

If you have any other questions we can help with, please let us know. 

Eric

[vinzzze]

Thank you @EricL  for the advice and for the pic showing the scarf cut. I was thinking what it is called as I seen similar illustration in my search for an alternative technique to fasten the bearer on top of the post. It will be a tight or small scarf as the gap is only 10mm. so 5mm each side.

I will ask my draftsman if I can use this method or if its acceptable to just scarf one side.

Re: nailing plate, would this plate Dunnings 200 x 70mm M10 Galvanised Bracket Plate - Bunnings Australia a better material to use than a knuckle nail plate?

I will ask my draftsman if we can add some sort of a post to add support to the ledger board if I opt to use a spacer. Perhaps a half stirrup post? The draftsman noted in the drawing that the fastener for the ledger should have a 300 mm cts per M12 bolt. However, there were no special notes or instruction if I use a spacer which I will also ask my draftsman.

My apologies for asking this again, does Bunnings sell a termite repellent membrane or an alternative material that would function as a termite barrier ?  

[EricL]

Hi @vinzzze

Using the Dunnings 200 x 70mm M10 Galvanised Bracket Plate - Bunnings Australia is a far better alternative to using a knuckle plate. Again, this is a question for your draftsman as one side will be installed at an angle with a scarf cut.

Your idea of putting support for the ledger is actually a great idea. If you're ever worried that the M12 bolts are not up to the task then support from the bottom is the best way to go. As for the termite membrane, I'm afraid there isn't one that does double duty. There is the Plascourse 300 x 30m x 500um Polyethylene Dampcourse, but it only provides a barrier one of the two necessary ingredients for a termite barrier. It does not have the necessary chemical protection that other barriers have.

I recommend getting quotes from your local pest specialist and seeing if any of them are rated to install a physical termite barrier at a reasonable cost.

Please keep us updated with your progress, we look forward to seeing the start of your decking project.

Eric