How to attach ledger board to concrete block foundation?

[JonoMilne]

Hi, I'm building a large, essentially L-shaped deck wrapped around our house. It starts by the sliding doors (north-west) with a very low 220mm profile, but the ground gently slopes away to the south and the east, so it will end about 600mm high. I posted last week about this on someone else's question, but I thought it was better I started my own thread.

I'm using a ledger board attached to a 3.56m west-facing concrete foundation, which will support 145x45 joists spanning 2m. So my question today (and this may not be my last!!) is about fixings. I'm looking to fit the 145x45 ledger board with four pairs of stainless steel screws (we're by the sea). I'm just wondering whether I need dynabolt-type fixings, or can use hex-head M12 masonry screws.

Also what length? Some guidance I've seen suggests the screws should be embedded 100mm into the concrete wall, which sounds a lot. By the time I've allowed for the 45mm thick ledger boards, 12mm packing and a couple of washers, that would come to a 160mm long screw, which seems excessive and perhaps hard to come by ...

Thanks in advance for any advice!!

[EricL]

Hello @JonoMilne 

I'm thinking more along the lines of using Ramset 300ml Chemset UltraFix Plus. This anchoring system has a Ramset M12 x 160mm Chemset Anchor Stud Galvanised - 10 Pack which should fulfil your need to anchor 100mm into the concrete foundation. However, I would like to suggest a possible alternative, I propose building the deck as a stand-alone floating frame. This will mean adding extra posts and anchoring the ledger to the bearers instead. The advantage of course is that there will be no structural load to your house or concrete foundation. 

Let me call on our experienced members @Dave-1, @AlanM52 and @Nailbag for their recommendations. 

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

Eric

[JonoMilne]

Thanks. I considered a full standalone deck but after talking with the builder (the ledger would be attached to the foundation of our new extension) I feel reasonably at-ease with attaching to the house.

I like the Ramset Chemset anchor stud solution, combined with Chemset UltraFix. But I do note that NZ building standard would tend to stipulate stainless steel fastenings rather than galvanised, because we're just 200m from the sea. Thoughts?

(This deck doesn't actually require a council building consent, because of its low profile, but I'm still cautious about ignoring the building code).

[EricL]

Hello @JonoMilne 

The longest stainless-steel bolt I could find on the website is the ZENITH M10 x 150mm Stainless Steel 304 Grade Hex Head Bolts And Nuts and for the Dynabolts there is the Ramset 10 x 100mm Stainless Steel DynaBolt Plus Hex Nut Masonry Anchor. I suggest speaking to your local stores hardware specialist and see if you can special order longer Dynabolts and Hex head bolts.

Let me call on our experienced members @TedBear, @JoeAzza and @Noyade for their recommendations.

If you need further assistance, please let us know.

Eric

[AlanM52]

Hi @JonoMilne,

Do you have some idea of what your house is 'sitting on' and the depth of the 'water table'.

Like almost everything houses are subjected to movement and the above will play a part to determine the amount of movement.

If you don't have that info I would play safe and follow @EricL's suggestion and do the stand alone frame thing.

BTW: I like your entry steps 😀

Cheers

[Dave-1]

Good Morning @JonoMilne 

Im another one for stand alone decking, it may cost a little more and also take a few more holes (note you cant dig straight next to the house as you will hit the foundation) but the benifits outweight the added complexity. No issue of transfer loading, no added forces anywhere. No issue with termitess following along the timber. 

Is teh wall you are wanting to put the ledger board on those bessa blocks? are they filled with concrete? If not then I would seriously NOT put the board on them. If its solid then what @EricL has suggested would be good. As to the longer bolts, have a look in your local industrial area for "fastenings" I am lucky enough to have one in the next suburb over and go in there for odd sized bolts and screws all the time. 

Looking at your pic, I am wondering what the difference in height between the earth and the support beams will be on the left? It looks like it will be close. I like at least a 50mm gap between the dirt and timber, if not 100mm, mostly for air flow.

We loooove questions and yeah when I have asked questions I have sometimes changed the way I am doing something due to a better way or a better sounding way. I have also taken it on board and still continued with my ideas The rule I have in my head "Its your place, you are the one doing the work, I am just an avid watcher" Cant wait to see the deck unfold! Please take lots of photos

Dave

[JonoMilne]

Thanks Dave, the Besser concrete blocks are concrete-filled, with rebar reinforcing. But given the views here, I’ll have a bit more of a think about chucking in three more piles in place of the ledger board. It wouldn’t be hard.

And yes, 100% re digging it a bit deeper on the left. I’d been mulling over the airflow last night, so your comment has helped me decide. A little more time on the spade in place of a gym visit!

Happy Christmas all!