Question regarding a low-level deck frame

[DJ11]

Hi All,

I am building a low level deck to be in flush with my current alfresco. It's a 5.5x4 deck, and I am using composite deck.  The write-ups from this community has been very helpful for me in designing my deck so far. However, I need some help from experts in this group in regard to the underlying timber frame design. I am not going with a bearer/joist setup otherwise i will have to excavate a lot, Its already a low ground so digging further will cause drainage issues. Hence, i will be just using tuffblock to support the joists. On the sides, i will have 90x90 footings concreted to the ground to provide extra support. For the joists I was thinking to use 140x45 H3 timber throughout initially, but budget is a major constraint and wanted to check if i can use 90x45 H3 instead and if it will be structurally very sound. That itself will save me at least $500 straight away. However, i don't want to go that way if it is structurally not strong. I will attach the design i have come up with for the frame.

Secondly, I am building an L-shaped in-built seating area on the deck, and i wanted to check what size wood you recommend that I should use to build the frame for the sitting area (70x35 or 70x45 or 90x35 or 90x45). I will be covering the frame with composite decks to match the deck so that it looks like one piece.

Any help on these queries will be greatly appreciated.

Please feel free to ask more questions, as i don't know if i have given all that you need to easily answer my queries.

Thanks in advance.

[EricL]

Hello @DJ11

Welcome to the Bunnings Workshop community. It's fantastic to have you join us, and thank you for sharing your question about your low-level deck.

Your deck framing plan looks great and it's good to hear that the discussions about low-level decks have helped you plan this out. One of the drawbacks of saving on footings is that parts of your deck will feel spongy. On the 4-meter side of your deck, your footings are at approximately just a little over 1.4-meters. I would suggest adding another foot to reduce this distance down to 1-meter. 

Will the 8-meter side of your deck frame be attached to your house? I only ask to make sure as I don't want to make any assumptions about your build. You can use 90x45 to build your deck frame and in order to stiffen the structure, I suggest installing noggins between the joists. As for the seats using 70x35 should be sufficient to build a seating frame for your guests and family members.

Before you go any further, I suggest checking with your local council on the rules and regulations of building a low-level deck. Especially the rules on size, height and when attaching a structure to your existing house. Let me call on my colleague @MitchellMc so that he can have a look at your framing plan as well. 

My number one tip for your build is to make sure that the drainage under your deck is totally taken care of before you put that first Tuffblock on the ground. 

Please keep us updated with your progress, we look forward to seeing the start of your low-level deck project.

Eric

[DJ11]

Hi @EricL ,

Thank you so much for the warm welcome and for the great advice. Its a big relief to know that 90x45 will work for my frame. Based on your advise I will add another line of concreted footings going through the middle of the frame and space the tuffblocks just a meter apart. In regards to noggins I just missed to put them in the design but i will definitely be adding them to the frame. 

And to your question regarding whether 8mtr side would be attached to the wall, yes it will be. I will be bolting them to the brick wall. Any suggestions what type of bolts should I use? As i have seen In several discussions most are not recommending dyna bolt for brick walls.

Secondly, As you have already understood drainage is the biggest problem I am facing. My plan is to install 2-3 drainage pits and connect them to the nearest storm water pipe. I am just assuming that there won't be any back flow during heavy rain. Kindly advice if there is a better way to do it. 

Again thanks a lot for your advice @EricL . Much appreciated. 

Cheers

DJ

[EricL]

Hi @DJ11

I suggest using Ramset Chemset System to mount your ledger onto your wall. This chemical in combination with its mounting studs is widely used in the construction industry and is very reliable. Ideally, I would recommend putting in a slope under the deck and then putting on weedmat with gravel on top to facilitate drainage. At the bottom of the slope, I propose installing a drain coil which you can then direct to your stormwater pipe.   

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

Eric

[DJ11]

Thanks @EricL . Will definitely get my hands on Ramset chemset system. While leveling up the ground what i noticed is that there is a very light slope with my current alfresco, against which i wanted my deck to be in flush with. The slope might be for a good water flow but my question is whether it is ok to build the deck with a slight slope so that it stays flush across the sides, also will aid rain water on the deck to flow away from the house. However, technically i dont know if thats a good idea or not. May be you can guide me on that.   

[MitchellMc]

Hi @DJ11,

There are no real issues with building a deck on a slope as long as you work the slope into the equation. 

I only have to add that, given the deck size and that you're connecting it to the house, I presume you'll submit plans to your local council for approval. You'll need to check whether you can use the Tuffblock system or if you'll need to use concrete footers specified for the soil type in your area.  

Mitchell

[DJ11]

hI @MitchellMc ,

Since the deck is below 25sqmtr and ground level council approval is not required. Secondly, i always preferred not to have the frame attached to the house it was just for the ease i wanted to do it  😁 but it looks like i am just going to have concreted footers to have more stability. 

[Duck]

 Thanks for the previous post on low level deck.

I am continuing a deck as in photo. The space between original deck and post is 2700mm. Thinking tuff blocks in the middle, but now thinking concrete. Opinion?

[EricL]

Hello @Duck

Welcome to the Bunnings Workshop community. It's fantastic to have you join us, and thank you for sharing your question about your low-level deck.

It all depends on your deck height measurements. The TuffBlock 300 x 300 x 90mm Instant Foundation System Deck Support will provide you with a height of 90mm, if you include the frame for example which is 90mm and the thickness of the decking panel 19mm, it will give you a total of 199mm. On the condition that your current deck is that high then it would be ideal to use it.

However, I suggest using the Builders Edge Pedestal system if your deck is higher. It is adjustable in height and can take timber frames of various sizes. Please keep in mind that the pedestal system will need to be used with pavers and the ground has to be compacted as well. Even though it is a small area, I recommend still putting in a slope so that you will have adequate drainage for the area.

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

Eric

[Duck]

Fantastic info, thank you very much. You say use pavers… as a footing, after compacting the ground underneath, I presume?

Drainage is not a problem, as the whole area is covered and the previous owners installed adequate drainage.

cheers

Mark