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Help please. I have been ruminating over this for quite some time and can’t decide what’s the best way to build my floating deck.
PLAN SO FAR
- Decking boards will be running parallel to the sliding door
- Picture framing
- 90 mm merbau decking boards (apparently less subject to cupping in low profile decks)
- Adjustable (or fixed) pedestal supports
QUESTIONS
1. How would you suggest I frame my deck so as not to block the weep holes and keeping maximum support for the picture framing and so people can step at the edge?
2. Should I deck over the brick sil or just deck up to it?
3. Should I make the finished deck height level with brick sil or some amount lower?
4. Given my height is restricted to approximately 190 mm if the deck is going to be flushed with the brick sil what framing members should I use?
Hi @maker_m82,
The first thing I note is your decision to use 90mm merbau decking. I should note that our 90mm merbau decking's installation guide recommends a minimum ground clearance of 400mm, so if you were to use it in this situation, it would likely not be covered by the warranty. If instead, you used Ekodeck Decking, the minimum ground clearance is 90mm, which would be fine with your project. Ultimately, you could still use the merbau, but you would not be covered by a warranty if there were issues deemed to be due to the proximity to the ground.
To frame your deck up to the brick wall without blocking the weep holes, I'd suggest your joists should not have a rim board along the end; instead, the joists should butt into the brick wall with blocking between them around 150-200mm back from the wall. Something along the lines of this -
You would be better off having the decking boards finish flush against the brick sill because they are meant to allow water to drain away from the door. If you installed decking over the top of them, you would be removing this function by creating a flat surface over them.
Flush with the brick sill is fine, but there should be a gap between the timber and the brick that will allow water to drain through.
Due to the limited height, it would be best to use 90x45 framing, as with a 19-22mm thick decking board, this will leave you with approximately 40mm beneath the framing, which would allow you to use Builders Edge 35 - 60mm Smallfoot Pedestal Feet for support.
90 x 45mm Outdoor Framing H3 Treated Pine is a common choice for low-level decks, but if you want to ensure your deck lasts as long as possible, I'd suggest using 90 x 45mm H4 Treated Pine as it is treated for use in close proximity and direct contact with the ground.
Let me know what you think. I am more than happy to assist further with design and materials.
Jacob
Hi @JacobZ, cheers for responding.
Im not worried about warranty. My budget doesn’t allow for composite boards as they are almost 3x the cost.
The specrite fact sheet does allow for lower than 400mm however it states that more ventilation must be considered. This is why I’ve chosen 90x45 instead of 140x45.
As for the air gap clearance, we reach different values on that. Am I overlooking some.
190-22-90=78. My clearance would be 78mm from the concrete the bottom of the framing.
As H4 framing, Bunnings can only special order this (from what I’ve seen) and I’ve been quoted long lead times with anything “special order”.
Also h4 is almost 2x the price.
Is the benefit of using H4 worth the extra expense and lead times or is it only marginal increase in benefit based on my 78mm clearance?
Another question I have is how to builders justify using 90 x 45 joists in a single layer deck construction when in that particular layout the joists are actually acting as bearers and according to bearer span tables, a 90x45 bearer should be doubled.
Final question (for now haha)
How do I frame the overhang along the left of the deck so the pedestals can’t be seen.
in the picture I’ve added the pedestals on the left outer most joist, cantilevered the bottom rim board out to support the deck edge (black) but I can’t work out a structural way to support it at the top since I can’t use a rim board the same way due to the weep holes. I thought about using blocking, but blocking would not provide the same structural support at the cantilevered rim board I don’t think.
What do you suggest in this situation.
Hi @maker_m82,
If you're not worried about the warranty, then you can use the merbau. I just thought I'd mention it to make sure you were aware.
Yes, you are right about the clearance. I was mentally working with the idea you had 150mm of height to work with and didn't think to double-check. You would have 78mm of clearance if you are using 22 mm-thick decking boards.
I always recommend using H4 on these low-level decks because there is always going to be potential for rot. After all, the airflow beneath the deck is limited, so moisture can build up beneath the deck, and H4 timber is treated with a fungicide that will help prevent the frame from rotting in damp conditions. You can certainly use H3 framing, but it just won't handle the moisture as well as H4. Again, I just thought I'd mention there are other options so that you are aware.
In this layout, the 90x45s are not actually acting as bearers. A bearer becomes a bearer when it is directly supporting other joists through a structural connection, whether it is with a joist hanger or by sitting on top of the bearer. In this layout, as each joist is directly supported by the pedestals beneath it, you would use the joist span tables to determine where the supports need to sit. So, using the Hyne Timber Joist Span Table as a reference, you would need a pedestal every 1400mm under each joist.
In this situation, I would suggest you create a double joist by adding a 100mm or so wide piece of blocking every 450mm and then set the pedestals underneath the inside joist. The overhang is minimal and would not be a concern structurally, but still enough to cover your pedestal feet.
Let me know what you think and if you have any further questions or concerns, please don't hesitate to add them to the discussion.
Jacob
