Trying to get a straight answer on the correct height a concrete perimeter path should be laid below damp course. I've spoken with numerous people and been given a range of answers ranging from minimum 15mm below (from our pest control company), to min. 75mm below which appears to be the most common response.
We're in SA and from reading the Building Codes from what I can tell it's a minimum of 50mm below damp course level if it's a solid concrete path. We'll be running it on a 50mm fall away from the house with a path 1 metre wide.
Our site supervisor tells us it's ok to have it sitting at 20-30mm below because of the termite protection barrier that's been laid on the slab perimeter directly below the damp course.
For obvious reasons I don't want to be voiding any structural warranties if I lay the path too high but for asthetics (and other landscaping reasons) I would ideally like the path as high as possible.
Keen for any input please...
Perimeter Path height below dampcourse
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The BCA Part 2 which is also Part 2 of the NCC references AS 3700. You can download the current (2016) three part NCC free of charge.
Australian Standards have to be purchased but Googling AS 3700 will bring up a lot of references but it must be realised that the BCA is the primary document and has hierarchy...this is important as you read further through this post.
AS 3700 states that the Damp-Proof Course must be at least 75 mm above finished surface level of adjacent paved, concreted or landscaped areas that slope away from the wall or...
50 mm above finished paved or concreted areas sloping at least 50 mm over the first 1 m from the building and protected from the direct effects of the weather by a carport, verandah or similar.
At least 150 mm above the adjacent finished ground in all other cases.
HOWEVER...there is a South Australian variation in the BCA Part 2 3.3.4.0 that states that in low rainfall intensity areas where the site classification is A, S, M, M-D, H, H1, H2, H-D, H1-D or H2-D in accordance with AS 2870, the height of the damp-proof course may be 15 mm above finished paved, concreted or landscaped areas.
A low rainfall intensity area is classified as an area having an average Recurrence Interval (ARI) of 120 mm/hr or less. Adelaide is a low rainfall intensity area.
You need to check whether this height will void your termite proofing warranty if applicable.
I personally think that having a 15mm gap is sailing a tad too close to the wind.
Australian Standards have to be purchased but Googling AS 3700 will bring up a lot of references but it must be realised that the BCA is the primary document and has hierarchy...this is important as you read further through this post.
AS 3700 states that the Damp-Proof Course must be at least 75 mm above finished surface level of adjacent paved, concreted or landscaped areas that slope away from the wall or...
50 mm above finished paved or concreted areas sloping at least 50 mm over the first 1 m from the building and protected from the direct effects of the weather by a carport, verandah or similar.
At least 150 mm above the adjacent finished ground in all other cases.
HOWEVER...there is a South Australian variation in the BCA Part 2 3.3.4.0 that states that in low rainfall intensity areas where the site classification is A, S, M, M-D, H, H1, H2, H-D, H1-D or H2-D in accordance with AS 2870, the height of the damp-proof course may be 15 mm above finished paved, concreted or landscaped areas.
A low rainfall intensity area is classified as an area having an average Recurrence Interval (ARI) of 120 mm/hr or less. Adelaide is a low rainfall intensity area.
You need to check whether this height will void your termite proofing warranty if applicable.
I personally think that having a 15mm gap is sailing a tad too close to the wind.
Full credit to you SaveH2O, you certainly know your stuff! I'm inclined to err on the side of caution and ask my concreter to set the levels at 25mm and then I'll have a 10mm tolerance for any places where he creeps a bit higher. The pest control company has already confirmed "no less than 15mm" for them to not void their warranty.
Thanks again for your assistance, very helpful!
Thanks again for your assistance, very helpful!
I'm inclined to err on the side of caution and ask my concreter to set the levels at 25mm and then I'll have a 10mm tolerance for any places where he creeps a bit higher.
I'm with you. South Australia will be having a lot more very windy wet periods from now on due to the weakening pressure gradient between the South Pole and the equator allowing the South Polar jet streams to drift north.
Um, would you believe me if I said you took the words out of my mouth?! lol
Just a reminder that if the path will have an Overflow Relief Gully (ORG), there are clearances that must also be observed.
The spill level (the surrounding surface) must be a minimum of 150mm lower than the lowest fixture connected to the drain, this will be either a floor waste or the shower drain. The lowest fixture will be level with the bottom of your weep holes.
The regulations also state that where the 150mm minimum height cannot be achieved, a reflux valve must be installed in addition to the ORG.
Another thing to note is that the BCA also allows an impermeable path slope of 25mm over the first metre in a low rainfall intensity area.
The rainfall intensity is based on an average intensity over a 5 minute period. As an example, an area with a 1:20 ARI of 120mm/hr (2mm/min) would need to record 10mm over a 5 minute rain intensity duration to register a 1:20 storm event.
NCC 2016 Building Code of Australia - Volume Two Page 112
3.1.2.3 Surface water drainage
Surface water must be diverted away from Class 1 buildings as follows:
(a) Slab-on-ground — finished ground level adjacent to buildings:
the external finished surface surrounding the slab must be drained to move surface water away from the building and graded to give a slope of not less than (see Figure 3.1.2.2)—
(i) 25 mm over the first 1 m from the building in low rainfall intensity areas for surfaces that are reasonably impermeable (such as concrete or clay paving); or
(ii) 50 mm over the first 1 m from the building in any other case.
The thread linked below may also interest you.
viewtopic.php?t=89573&f=1&p=1753118#p1753118
The spill level (the surrounding surface) must be a minimum of 150mm lower than the lowest fixture connected to the drain, this will be either a floor waste or the shower drain. The lowest fixture will be level with the bottom of your weep holes.
The regulations also state that where the 150mm minimum height cannot be achieved, a reflux valve must be installed in addition to the ORG.
Another thing to note is that the BCA also allows an impermeable path slope of 25mm over the first metre in a low rainfall intensity area.
The rainfall intensity is based on an average intensity over a 5 minute period. As an example, an area with a 1:20 ARI of 120mm/hr (2mm/min) would need to record 10mm over a 5 minute rain intensity duration to register a 1:20 storm event.
NCC 2016 Building Code of Australia - Volume Two Page 112
3.1.2.3 Surface water drainage
Surface water must be diverted away from Class 1 buildings as follows:
(a) Slab-on-ground — finished ground level adjacent to buildings:
the external finished surface surrounding the slab must be drained to move surface water away from the building and graded to give a slope of not less than (see Figure 3.1.2.2)—
(i) 25 mm over the first 1 m from the building in low rainfall intensity areas for surfaces that are reasonably impermeable (such as concrete or clay paving); or
(ii) 50 mm over the first 1 m from the building in any other case.
The thread linked below may also interest you.
viewtopic.php?t=89573&f=1&p=1753118#p1753118
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