How to build frame for low-level deck and paved area?

[jimmyA]

Hi All, 

Appreciate any help given. I've built a few decks in the past where clearance hasn't been a problem so we've gone for the traditional setup of joists over bearers.

This time the area I'm working on (I'm home owner by the way, just a DIYer) an area with an existing concrete slab.

The height from the slab to the back door is only 180mm so I'm not sure if I should go with small gauge timbers for traditional joists on bearers, or go with sturdier joists in a single layer structure as explained here: How to build a low-level deck | Bunnings Workshop community

The slab is only a small portion that I want to deck over so I'd be removing all of the existing pavers and digging / concreting the appropriate footings everywhere else.

Given the size of the deck, I'm just a bit unsure of the best way to go. I'd assume heavier timbers in a single layer approach, but how would I divide the deck up?

In images below are a bit back the front. For the deck image, the width of 8800mm would be up against (but separate from) the house with the laundry door and extends over and across the side gate.

The 7200mm edge in that image comes towards us and below the sliding doors. I would need to build a single step/landing from the deck up to the level of the sliding door. 

You can see that there is an existing roofed area so I'll need to do some joinery around those uprights.

I'd also like to do the picture frame style on the borders.

The 3200x3200 area that I've left out will step down into a paved area.

I'm going to use these for that area: Brighton Masonry 400 x 400 x 42mm Pearl Premium Pave - Bunnings Australia

In short, I'm after advice on the best way to frame this!

For the decking I'm currently leaning towards: Ekodeck 137 x 23 x 5400mm Backbeach / Leatherwood Plus Designer Series Composite Decking - Bunnings ...

[MitchellMc]

Welcome to the Bunnings Workshop community @jimmyA. It's wonderful that you've joined us, and many thanks for your question about low-level decks.

If you look through the many low-level decking projects our amazing members have contributed, you'll notice that using a single level approach is popular. I'd personally recommend you go with Treated Pine Outdoor Timber Framing 140 x 45mm, though economically wise, since this is such a large deck, you could consider dropping to Treated Pine Outdoor Timber Framing 90 x 45mm. In either case, you'd require those timbers evenly spaced across the eight-metre width at around 430mm centres. That would be 21 lengths. Since you'd like to picture frame the deck, you'll need to double-up and frame out the joists with additional timber. This allows you to not only nail off your decking but also additional space to place your picture frame onto and nail into.

For supports, since you have an overall height of 180mm, if you use 90mm timber and 19mm decking, you'll be left with 71mm to finish flush with the door sill. For the concreted area Builders Edge Pedestal Foot Bigfoot Xl 70 - 170mm would be perfect for a flush finish. If you're happy with a slight lip onto the doorsill, you could go with Builders Edge Pedestal Foot Smallfoot 35 - 60mm. These adjustable feet are perfect for counteracting any fall on your slab to get a level finish on the deck. 

Ekodeck would be a fantastic choice for a low-level deck. As per Adam's article on low-level decks, I'd advise you to put some drainage measures into place for the soil area. You might wish to grade the underlying soil to send the water into that existing drainage channel.

Please let me know if you have any questions.

Mitchell

[shauny]

@jimmyA  What software did you draw your deck up in? I like your design.

[jimmyA]

Hi @shauny ,

This is the free designer here: Deck Designer, TimberTech Azek composite Decking, balustrade, Porch

@MitchellMc - thanks for your suggestions - I was planning on doing some french drains to run down and meet up with the main drain channel.

I think i'll draft a design up using the 140 x 45mm. One question I have is about the size of the bearer around the outside of the frame. In the article I linked it suggests a larger bearer compared to joist, I assume so you can use the hangers.

Given the 180mm height, I don't think there is a good size that would work? 

Also,  is a maximum span I should look at for the joists? How many sections or bearers should I divide the deck into or is that not necessary?

Thanks

[MitchellMc]

Hi @jimmyA,

There is no need to use a larger bearer around the outside of the frame unless the frame and/or joist aren't supported at appropriate intervals. A larger frame will be needed if you are spanning a large length unsupported. Hangers will work just fine with the same sized timber. 

You'll need to check online timber span tables and regulations to verify the exact span 140 x 45mm timber can go unsupported. On a low-level deck, supports at 1500mm would be a fairly safe bet, though.

The bearers should be spaced at 450mm across the deck. Once again, you could push that further, but the larger the gap the decking has to span, the more spring there will be to it. If you had them at 1000mm, you'd end up with a spongy deck.

Please let me know if you have any questions.

Mitchell

[jimmyA]

Hi @MitchellMc

Here is what I've come up with from a framing perspective.

Joists to be connected to the bearers via hangers.

For the picture frame edges I allowed an extra joist as those ecodeck boards are 137mm. In terms of supporting the doubled joists, would you recommend a stirrup such as Pryda Post Anchor Full Stirrup 65 x 90mm M10 Box 10 - Bunnings Australia or is there a better option?  Also if I were to support those double joists would there be any need to support the outer most bearer on either end?

For the rest of the joists I will look at the options you already posted.

Finally given the span lengths would I be joining two joists end to end on a stirrup/pedestal? Should I use any other product to secure that connection?

[EricL]

Hi @jimmyA

My only concern in using the Pryda Post Anchor Full Stirrup 65 x 90mm M10 is that it is not height adjustable. I recommend going with @MitchellMc's suggestion of using the Builders Edge Pedestal Foot Bigfoot Xl 70 - 170mm. It is rated to carry 800kg and will also allow you to adjust its height.

I will have to confer with my colleague about placing support on the outer bearer and the double joist on a single pedestal. As soon as I have more information, I will let you know.

Eric

[jimmyA]

Thanks @EricL 

I'm happy to go with the pedestal option, I just didn't think it would take 2x45mm W joists.

According to the spec it does though!

fc35e6b5dc9a4eefb7ff5f7eb4f6c9e8 (bunnings.com.au)

Only issue with that one is height. I assume 70mm is the lowest height of the pedestal itself - timber height needs to be added to this?

I was planning on using 145x45mm for the joists, but with those pedestals maybe I should consider using 90x45. I'd need a lot more pedestals though - every 850-1000mm depending on load rating.

I'd very much appreciate your answer on the setup for the outside bearer/joist pedestals!

Thanks again

[MitchellMc]

Hi @jimmyA,

The post support will be a good option if you don't need the adjustability. 70mm is the lowest height for the adjustable foot, and timber height is added to it.

The outside timber is connected to the doubled-up bearer, and its supports are all that's needed.

Using the pedestal is fine for under the joists joins. However, I'd suggest you grave the pieces together with another short length of timber. I'll include an image below to illustrate.

Mitchell

[jimmyA]

That's awesome! Thanks for all the support and suggestions @MitchellMc @EricL 

Will plan out the pedestal locations and then it's time to get to work