Hello dear building forum community,
My wife and I own an end townhouse, and we would like to build a wooden deck on the garden side. We have a side exit there, so it seems like a perfect spot.
However, we have a major issue: underneath the planned deck area, there are utility lines (electricity and water) located about 80 cm (31.5 inches) deep. Our soil is former farmland, a compacted mix of clay and loam with a high content of stones, ranging from pebbles to sizable blocks.
What type of foundation should we plan for this? We have read a lot already—everything from placing the deck directly on the ground, using driven ground screws, a gravel foundation of only 40 cm (16 inches), up to a full 80 cm (31.5 inches) deep pier or strip foundation, which is said to be frost-resistant. But the utility lines might be in the way of deeper foundations!
My latest idea was a 40 cm to 60 cm (16 to 24 inches) foundation on adjustable screw supports, which could allow me to easily correct any unevenness caused by frost movement.
But what would be the most sensible and safest solution in our situation? Are there any experiences or recommendations regarding this?
I am quite uncertain because once it’s done, there is no going back without additional expenses!
What can I do and what should I do?
My wife and I own an end townhouse, and we would like to build a wooden deck on the garden side. We have a side exit there, so it seems like a perfect spot.
However, we have a major issue: underneath the planned deck area, there are utility lines (electricity and water) located about 80 cm (31.5 inches) deep. Our soil is former farmland, a compacted mix of clay and loam with a high content of stones, ranging from pebbles to sizable blocks.
What type of foundation should we plan for this? We have read a lot already—everything from placing the deck directly on the ground, using driven ground screws, a gravel foundation of only 40 cm (16 inches), up to a full 80 cm (31.5 inches) deep pier or strip foundation, which is said to be frost-resistant. But the utility lines might be in the way of deeper foundations!
My latest idea was a 40 cm to 60 cm (16 to 24 inches) foundation on adjustable screw supports, which could allow me to easily correct any unevenness caused by frost movement.
But what would be the most sensible and safest solution in our situation? Are there any experiences or recommendations regarding this?
I am quite uncertain because once it’s done, there is no going back without additional expenses!
What can I do and what should I do?
nordanney schrieb:
This is how we built our terrace. About 30-40cm (12-16 inches) of compacted gravel, then placed on mortar bags or stones. This is actually the second terrace in the last 10 years. No point, strip, or any other type of foundation.
Finished, it looks like this:The mother of all terraces. Amazing.
Bauexperte schrieb:
If the planned terrace encroaches on the setback area, it is questionable whether you are even allowed to build it This has already been discussed with the building authority. As long as we stay within 3 m (10 feet) in depth, we could theoretically build a terrace around the house on our property, but it is only supposed to be 3 by 7 m (10 by 23 feet).
Great terrace in the pictures. Is the ground made of clay soil? I would like to do it similarly, but when it rains here, the soil becomes muddy and soft. I’m concerned this could cause problems related to weight and stability. Everyone talks about a frost protection depth of 80 cm (31 inches), so why only 30–40 cm (12–16 inches)? Have there never been any problems?
The utility lines run at 80 cm (31 inches) and are located only within the last meter of the terrace plan, so not completely in the center. But I also think it would definitely be an advantage to keep the foundation structure minimal, so that if repairs are needed, a heavy foundation won’t be in the way. That’s why I really like the terrace in the pictures—quick to build, but also quick to remove, relatively speaking.
Thanks for all the constructive replies.
EveundGerd6 May 2015 21:28Our ground behaves a bit like cake batter. Therefore, we had to excavate to a depth of nearly 1.50 m (5 feet) and build up almost 1.60 m (5 feet 3 inches). Our terrace is currently under construction, and as a base for our paving and the path around the house, our civil engineer/landscape contractor has laid and repeatedly compacted lava. Now the edging stones are in place, and hopefully the terrace will be usable in two weeks.
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