Is a free standing patio roof a bad idea?

Question

This is located in Auckland, New Zealand. We don't get snow here, but we do get fairly strong winds. I'm looking for some conceptual design advice...

I'm looking to build a deck measuring 8 meters wide, about 4 meters deep (off the face of the house). Now the main complication is where the deck and the house join, will be half house, half conservatory, which is glass and aluminum.

I will also have a roof on the deck. Sloped, maybe 2.5m high on the high end. The deck is also going to be very very low on the ground, which is a totally flat site.

Trying to "attach" the deck to the house looks very very difficult. Am I being naïve thinking it could be free standing?

EDIT: OK, I've added a privative picture.

The deck is only maybe 200mm high? It's not the stability of the deck floor that I'm worried about.. it's the roof line.

For simplicity I want a mono pitch roof of UV resistant poly carbonate sheeting - the sun is brutal here.

The new Zealand Building standard for this is NZS3604, which really doesn't have much to say on the matter of decks on the ground. When decks get over a meter in height, it's a whole different ballgame. As per the standard: "Wind Bracing demand for decks may be ignored.

So really ... it's the roof.

If the roof is free standing, and winds are high, there could be some lateral movement which is a problem. But to secure the deck roof to the house structure is complicated by the conservatory.

Thoughts?

Answer 1

The traditional way to build a deck is extremely securely attached to the house and with a very strong foundation for the support columns. That is a must for safety when the floor is a few meters above the ground.

However, there are two other alternatives when the floor of the deck is relatively close to the ground:

• Separate Structure

A separate structure is essentially building a building next to an existing building. They are not attached, which helps in earthquakes, storms, etc. because you don't have to worry about the coming apart from each other - they are already separate. However, there are likely some rules as to how close they can be, and having a deck that is more than a few centimeters away from your house may not work very well. But a full structure with a real foundation may be needed in order to properly support a roof so that the whole thing doesn't blow away or collapse in a storm.

• Floating Deck

A floating deck is not attached to the house and it is not attached to the ground! Concrete blocks sitting on the ground support the frame of the deck. This is inexpensive and easy to build (no concrete to pour). However, there are limitations to the overall size, height from the ground (for obvious safety reasons) and I would definitely be concerned about a roof that could act as a sail and pull the structure off the supporting blocks.

A lot of this is jurisdiction dependent. Check around the area to see what other people have done. And check with your local building department to find out what is allowed and what permits are required. In my area, regular decks require a full permit and inspection process, but floating decks below a certain size (much smaller than what you are planning) don't require a permit at all.

Answer 2

In one aspect it's good that you build it without relying on the house to support it as doing otherwise may place additional load on the house which it was not built / rated to support.

It's certainly possible to build it freestanding, but there are a variety of structural things you'll need to take into consideration like how the supports are secured into the ground, shear, uplift, etc.

Drawing up plans of what you're thinking would be ideal to get more targeted feedback. It'll also be important that if the house and patio are effectively freestanding next to each other, that they be designed so that there are not damaging (acute or chronic) collisions / rubbing during wind or seismic events.