How to build a timber ramp over stormwater pipe?

[Jerrod]

I want to build a timber ramp over a stormwater pipe that crosses a concrete pathway next to the house. The ramp needs to be 850mm wide (it is not possible to make it any wider than 850, and I don't want to make it any narrower). The top of the stormwater pipe is 225mm above the path. So the ramp needs to go from 0mm (path level), up to at least 225mm, then back down to 0mm.

I was thinking of using some 200 x 50 H4 treated pine sleepers (cut on an angle and stacked on top of each other) to support some merbau decking boards.

I understand that decking is usually laid over joists at 450mm centres.

If I space the sleepers apart at 450mm centres, the merbau decking will have a 175mm cantilever (or overhang) on either side. I've never read of a deck with cantilevered decking, but since this ramp is quite low and the overhang is only 175mm, I thought that might be OK.

Am I wrong here? Is there a risk of someone standing near the end of a merbau board and it collapsing?

I could modify the design so that it uses three sleepers (instead of 2) to support the merbau decking. This would result in an overhang or cantilever of only 100mm. But maybe that is still too much? Three big sleepers seems like overkill for such a low ramp.

What if I put a galvanised angle bracket under each piece of decking, on the outside of each sleeper, to reduce the overhang distance a bit? (eg a Carinya 75 x 50 x 20 x 4mm Galvanised Angle Bracket would reduce the overhang to 100mm with 2 sleepers, or to 25mm with three sleepers).

The Sketchup image shows a section of the pipe crossing the path, as well as some dashed lines (guides) indicating where the sleepers would go, at 450 centres, starting from the centre of the ramp. 850mm is the total width of the ramp.

There are some metal standoffs supporting the stormwater pipe and keeping it off the path. Their locations (which are already set) make positioning the sleepers a little more tricky. They could be repositioned if necessary, but I'd prefer not to.

The ramp would have a gradient of 1:12 (or maybe 1:10) on either side.

[Jerrod]

Hi @EricL 

Thanks very much for your advice and encouragement.

Is there a treatment for the cut ends of the pine sleepers that can be applied with a brush, instead of in an aerosol can? I'm trying to reduce the amount of toxic chemicals wafting around the garden.

Are there any suitable treatment products that are low VOC?

How should I treat the cut ends of the Merbau?

Jerrod

[Nailbag]

Your revised plan looks terrific @Jerrod and yes Merbau is a far better long term option. Using protectadek between the boards and sleepers will increase life as well.

Nailbag

[MitchellMc]

Hi @Jerrod,

You could use a water-based bitumen paint for the cut ends of the sleepers. It is not smelly and is a water cleanup, unlike old tar bitumen. It's not as effective as re-treating them, but it will help seal the ends. Alternatively you could paint them with exterior paint.

Merbau doesn't need re-sealing, but you can coat the ends and the surfaces with decking oil.

Please let us know if you need further assistance.

Mitchell

[Jerrod]

Thanks @MitchellMc that water based bitumen paint sounds good. And thanks for the merbau info.

[Jerrod]

I bought the sleepers and the merbau last week. I'm slowly working through doing all the cuts in the sleepers. I've noticed that some of the sleepers are at least 50% heavier than the others, which I assume means they are waterlogged. Those waterlogged sleepers are much more difficult to cut with my Japanese ryoba hand saw than the drier sleepers. For the crosscuts and cutting notches, the hand saw has been adequate. But for the long, angled rip cuts, the hand saw was getting bound up as I got deeper into the rip cut, and waxing the saw blade didn't help. I had to use a jigsaw (instead of the hand saw) to do the whole 2m+ rip cut. Then I've had to use a power planer to smooth out the wobbly edge. I tried other saws like the Bahco ERGO™ Superior™ NXT 550mm Handsaw, but that didn't cut any further than the Japanese saw. I do have a circular saw, but I've only ever used it once, and I'd prefer to avoid using it for something tricky like cutting through thick, waterlogged timber.

Also, the small additional pieces near the apex of the ramp are OK, but matching the slope of the sleeper below is a bit fiddly. I've had to use the power planer to clean those up.

I have a few more questions.

1. Should I put something under the sleepers to keep them off the concrete path, or will they be OK, given that they are H4 treated and that I will be putting bitumen paint onto any cut surfaces?

2. I've seen that some people use galvanised angle brackets to raise their deck joists 10mm off the concrete, but I was thinking of screwing 10mm plastic window packers to the undersides of the sleepers. Would that work? Is that even necessary?

3. I've got to make a second set of ramps over a second stormwater pipe elsewhere. This second one is about 15mm lower than the first one. So that I don't have to cut the small extra bits near the apex of the ramps, I was thinking of different timber for this second set of ramps. Instead of H4 200 x 50mm sleepers, I was thinking of using 240 x 45mm Outdoor Framing H3 Treated Pine. Their 240mm height means I would not have to add any extra bits of wood at the ramp apex to make up the necessary height, so less cutting and less fiddly work. Is this a good idea, or should I stick with the H4 sleepers, because of the higher level of CCA treatment in H4 vs H3?

4. If I do use H3 framing pine, will that be OK to be resting on the concrete path, or should I use galvanised angle brackets or plastic window packers to raise it 10mm off the path?

5. Could I use a reciprocating saw for the long, angled rip cuts through the waterlogged sleepers? I'd guess it would be faster than the jigsaw, but would the shoe of the recipro saw hide the cut line and make it difficult to saw straight?

[MitchellMc]

It sounds like you've made some great progress @Jerrod.

The sleepers are fine to sit on the ground, especially if you reseal that cut edge as they are H4-treated.

Using 240 x 45mm timber for your other ramp is ok, but since it's only H3-treated for above-ground use, it really shouldn't sit on the ground, so plastic packers screwed to the bottom or raised on brackets would be the way to go. Also, you can paint the bottom with bitumen paint for additional protection.

You're right that a reciprocated saw would cut faster, but due to the long thin blade it might have a tendency to track offline. I'd keep going with the jigsaw and perhaps pick a blade with large and fewer teeth which will have less difficulty getting through the timber.

Please let me know if you have further questions.

Mitchell

[Jerrod]

Thanks for your advice @MitchellMc .

I've now completed the first pair of ramps. I've learned a few lessons that I hope to implement in the second pair.

One of them is to cut the support joists so that they don't taper down to nothing at the tips, because there is not enough wood to screw into. In the next version, I'll taper them down to a thickness of 10mm, so that I can use 25mm or 30mm stainless screws to attach the decking to them. Unfortunately the shortest decking screws seem to be 50mm, so I'll have to use stainless steel hinge screws that come in shorter lengths.

Here is a 3D image of what I mean.