How to build a pergola attached to the house?

[pasquaj]

Hello Bunnings

I am researching a project that I am going to undertake shortly. I am wanting to attach a timber pergola to a house. The pergola will be

have width of approx. 5.4m x depth of 2m

a) A H3 ledger board of 190mm x 45mm x 5,4m will be attached to the house with appropriate bolts.

b) Two (or more if required) H4 posts will be concreted into the ground and will have a final height of 2.4m.

c) A main H3 beam will be attached to these two posts (or more), I am thinking 240mm x 45mm x 5.4m.

d) The posts do not necessarily have to be positioned at the ends of the 5.4m main beam.  They can be positioned in for some overhang of the main beam.

e) 140mm x 45mm H3 rafters will be attached across the ledger board to the main beam.

f) H3 purlins 70mm x 35mm will be attached  across the rafters.

g) A lightweight polycarbonate roofing will be installed. 

h). The pergola will have a 5 degree pitch.

It’s a little confusing trying to decipher span tables. For this project I have 3 questions

     
1. What size posts should I use?

2. How many posts should I use. (I note two above ? need an additional post). 

3. Is a 240mm x 45mm x 5.4m main beam suitable for attachment to two posts (or more required).

Hoping you can advise.

Regards John

[EricL]

Hello @pasquaj 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your pergola project.

Your pergola project sounds great! I’m happy to offer some advice to help you get started, but keep in mind that for a structure like this, it’s always best to have it certified by a draftsperson or engineer. They’ll make sure everything is structurally sound and meets council requirements. It’s also a good idea to check with your local council about any size or home attachment rules. If you’re looking for a simpler approach, building it as a free-standing pergola might save you some extra approvals and planning headaches.
 

For the posts, I propose something like 100mm x 100mm H4-treated timber should be a solid choice but double-check based on your final design. As for the number of posts, having just two over a 5.4m span might not be enough, so adding a third post in the middle would give the beam extra support and help prevent sagging.
 

Your main beam at 240mm x 45mm is strong, but over a 5.4m span, it might need extra reinforcement if only using two posts. I recommend going with three posts, to make it more stable.

Since you’re using lightweight polycarbonate roofing, the load won’t be as heavy as other materials, but it’s always good to get professional confirmation on spans and fixing methods.

If you need further assistance, please let us know.

Eric

[pasquaj]

Hello.
I am planning to build a pergola approx 12sqm (6m wide x 2m deep).

I note several classifications H (3-4), F (5-17),  MGP10.

I am familiar with the H3 and  H4 that Bunnings sell.

Then there is seasoned and unseasoned classification.
What does one buy for such a project? 
regards John

[Jewelleryrescue]

Hi @pasquaj 

Yes all those specifications are a nightmare  to think about as your experiance grows.

I will try and help several of these terms can apply to timber at the same time so just look at them one at a time.

Generally most of the wood you buy will be pre seasoned or kiln dried  at hardware stores that means the moisture level in raw wood is reduced and the wood will shrink by around 10% this also reduces the chance of timber warping.  Vs buying direct from a logging yard you might get unseasoned and if you built a deck with that straight away the floor will shrink by 10% and cracks will appear,

F(5-17) as you mentioned refers to its structural grade eg  5 is weaker than 12 etc. F17 is used in the higher stress applications and is usually price accordingly.   But for use DIYers most timbers will suit our needs At Bunnings some timber will be rated as structural so that will be stronger than Non Structural.  It would be rare for DIYers to need to use structural wood but is optional/

MGP10 Stands for Machine Grade Pine  a rating making it strong and durable. Versatile use indoors, Lightweight, flexible nature,

Another term is DAR or just   " Dressed " all round this means the timber id generally cleaner straighter has less knots (Weak points and blemishes) and most of all has machined clean edges to a specific size. We pa.y more for this and would be mostly used where exposed timber is desired.

As you already know as you said H3 is treated pine for outdoors for pine off the ground and is wet occasionally

H4 is treated pine in the ground with some wet feet ie posts etc

H5 is treated pine for wet ground applications typically H5 is not common at hardware stores more H3 H4

So If your project out doors best to use Treated pine. H3 to H5 from dry to wet conditions.  

All timber can be used indoors  . Stronger look for Higher F rating,  smoother flatter look for dressed etc.

You can also paint a lesser timber etc to improve its weather resistance indoor timber can come outdoors etc.

[EricL]

Hello @pasquaj 

Thanks for sharing your question about timber classification.

It's fantastic that you you've received excellent advice from @Jewelleryrescue. The definitions and explanation that Jewelleryrescue has provided are very good. My best advice is to engage the services of a draftsperson or engineer to make sure that your plans are structurally sound. I also recommend checking the rules and regulations of your local council in regards to the size of your pergola. There might be size limitations which will require you to get a permit.   

If you have any other questions we can help with, please let us know. 

Eric