Patio

[JohnBishop]

Hi All,

I hope you are well.
I have a project to build this patio at the back and I already changed the design to simplify it a bit.

https://ibb.co/167c5RL
https://ibb.co/0cYvng0

The idea is to use 6 inch posts then 5 inch crossbeams in mortis and tendom on top of posts and 2x12 girders to secure the structure on the shorter distance.
I cannot support the structure on the house wall due to insulation.
The anchoring is pretty much squared away as I am going to use proper steel bases in concrete and some attached to existing concrete with resin anchors.
I am planning to use 2x10 rafters. Isn't this an overkill, I mean 2x12 girders and 2x10 rafters.
On top I install double layer polycarbonate sheets.
What do you think?

[dewaltdisney]

My thoughts are you need to think about wind resistance. This will be a heavy structure but unless you plot the likely directional wind forces it could cause big issues with lateral movement given the freaky weather we can have. The roof wall plate needs to be anchored to the wall and you could resin-fix a row of studdings into the house wall to bolt the structure to it. This would secure against sideways movement. You have 4" of brick so you can drill to most of this depth for your studs and the wall plate could be secured. Put washers between the wall and the plate to create a gap to allow air to circulate.

DWD

[JohnBishop]

My thoughts are you need to think about wind resistance. This will be a heavy structure but unless you plot the likely directional wind forces it could cause big issues with lateral movement given the freaky weather we can have. The roof wall plate needs to be anchored to the wall and you could resin-fix a row of studdings into the house wall to bolt the structure to it. This would secure against sideways movement. You have 4" of brick so you can drill to most of this depth for your studs and the wall plate could be secured. Put washers between the wall and the plate to create a gap to allow air to circulate.

DWD

I understand however I would want to avoid using the wall at all. I don't want to touch the wall due to the thermal bridging this would create.
I am building a pergola next in a similar fashion and I don't have any wall to support it on.
I don't understand why patio needs wall support while pergola does not and I see people building pergolas using only 5x5 posts or even less.
I actually saw one what looked like a weak structure to be honest but it wasn't taken down by these ~33mph sustained wind and 50mph gusts we had early this year.

Do you mean that under wind stress patio would keep hitting the wall?
I was thinking about leaving a gap between the two structures and install some sort of weather gasket (rubber or plastic)

There is a big shed next to the patio (on the 7 o'clock if you look from the front of the patio) that blocks most of the crazy wind going in north-east direction.
Shed's roof would be above patio's roof. Shed's roof slopes down slightly to the west while patio's slopes down to the south.

Do you mean this mortis and tendom is not sufficient for lateral forces and you would prefer 2 girders on each side of the post instead?

[dewaltdisney]

It is difficult to make observations from your description. I was only drawing your attention to the fact that the roof being open will get wind under and over it which could cause lateral or upward stresses. The fact it is not tied to the wall means that the uprights will take all the lateral stress. it will depend on how sheltered and its position in relation to the prevailing South Westerly winds which might be different where you live. It is just something to consider, it is your decision at the end of the day.

DWD

[JohnBishop]

It is difficult to make observations from your description. I was only drawing your attention to the fact that the roof being open will get wind under and over it which could cause lateral or upward stresses. The fact it is not tied to the wall means that the uprights will take all the lateral stress. it will depend on how sheltered and its position in relation to the prevailing South Westerly winds which might be different where you live. It is just something to consider, it is your decision at the end of the day.

DWD

Of course I understand the implications that is why I go for heavy duty bases resin with bolts into existing concrete and front posts will sit on bases that are embedded in concrete. This will make sure the wind won't lift the whole thing up. Lateral forces is another challenge.
I think I go for 6x6 crossbeams to make it even with 6x6 posts.
I think as long as I bolt it well together it should sustain the stresses. I reckon the polycarbonate sheets would crack and break sooner.

[dewaltdisney]

If I understand correctly the four corner support legs will be timber in steel floor mounts. I suspect that as it will not be tied to the wall it will have a degree of whip due to the natural flex in the wood. It might be necessary to put angle braces at the top corners to firm it up. Of course these could be retro fitted if it prooves to be unstable.

DWD

[JohnBishop]

If I understand correctly the four corner support legs will be timber in steel floor mounts. I suspect that as it will not be tied to the wall it will have a degree of whip due to the natural flex in the wood. It might be necessary to put angle braces at the top corners to firm it up. Of course these could be retro fitted if it prooves to be unstable.

DWD

I use these 3 different bases:
These two go next to the wall (I ordered one of each to see how good they are). Cheaper one is galvanised but 8mm steel, the other one is stainless but 5mm.
https://www.amazon.co.uk/dp/B08FQV9XYW? ... ct_details
https://www.ebay.co.uk/itm/175719585849
How far from the wall should I put them? I reckon I need some access to insert the bolts and to install the brackets? What brackets do you have in mind? I think since it's not supported on the wall it does not matter much just not too far and not too close.

then two of these go into new concrete for two "outer" posts so there is no way this can be ripped off the floor so the next is to make sure the joinery near the roof won't fail.
https://www.ebay.co.uk/itm/324527521877 ... WqwFAAAAAA

[dewaltdisney]

This is what I meant to stabilise any lateral whip https://kenaitimberframes.com/rustic-ti ... -assembly/

DWD

[JohnBishop]

Something like that. Make sense.
https://ibb.co/kc7jRMk

Should I reinforce 2x12 as well or is it an overkill?
https://ibb.co/MSb3g9V

I think I make all the crossbeams 6x6 as well.

[dewaltdisney]

I do not think it is necessary, the braces will not only add stability but they will strengthen the frame structure.

DWD

[JohnBishop]

I do not think it is necessary, the braces will not only add stability but they will strengthen the frame structure.

DWD

Ok, thank you
How far from the wall do you think? 6 inches?

[dewaltdisney]

As it will not be tied into the wall, I would think that would be fine. Take into account any roof eaves hang over to cover the wall to frame gap.

DWD

[JohnBishop]

Little update re this project. I have assessed the existing concrete and it looks like I will not be able to use the resin fixings because the concrete is not thick enough. Only about 4 inches which is 10cm but for the M10 fixings I will need at least 13cm and for M12 studs 18cm.
I will have to cut out the existing concrete and pour thicker bases.

I bought 4 of these galvanised bases that go into wet concrete. Not sure if these are strong enough though. It looks like the large bit of it is 5mm tick steel but the foot is only 3mm thick. How do you thi

I bought 3 different bases to inspect them individually. I think this one is the most heavy duty but this one needs holes and resin fixings. It is 7mm thick galvanised steel.
https://www.amazon.co.uk/dp/B08FQV9XYW? ... ct_details