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Build a lean to pergola

A pergola spanning the width of your patio offers you some shelter from the sun and brings some privacy from your neighbors.

Whenever you attach something to your home you risk causing damp problems. Unless your home is a bungalow and your pergola will join your home under the eaves you will have to take precautions.

The first is to ensure the pergola has a slight fall from your home so no rain water runs along the timbers and the second is to make sure their is a gap between your home and the support joist attached to it.

There are several safe methods used for attaching a joist to a house without risking damp problems. I always use a decent thickness of threaded rod fixed into the masonry with anchor resin. Here's how:

Make sure your 6x2 joist is nice and straight. If their is a slight bow, have it pointing upward.

We'll assume the pergola is to be 12ft long and spanning a patio 12ft wide.

For a 12ft long pergola you will need 10ft long joists. Lay a joist down and find the center by measuring and dividing by 2. Mark the center and drill a 3/8" hole 1" from the top and another 1" from the bottom.

Measure 1ft in from the end and drill 2 holes as before. Repeat for the other end.

Now, you are going to need a friend to help you here. One of you needs to hold the joist up against the wall as high as you can while the other person uses lengths of your roof trusses to wedge it up. Once its safe, you can let go.

Now measure up from the ground at one end and using the wedge to manoeuvre it, get it to roughly 8ft from the underside. Use a level to set the other side. Make sure you are happy its level, at the correct height and safely wedged into position.

Put a small masonry drill bit into your cordless so that it easily fits through the holes in your timber without disturbing it and very carefully mark your brickwork/render etc. with a small hole. You don't have to drill deep, you just want a starter for when you drill the hole proper.

Once you have marked all 6 holes you can take down the joist and drill the holes into your wall. Size M10 is plenty for this type of structure. The drill size is dependent on the type of anchor resin you use. Check the instructions carefully to make sure you use the right sized drill bit.

Once the drilling is done, removed any dust from the holes ready for the anchor resin and threaded bar.

Some hardware stores sell the bars in short lengths but we buy ours long and cut to size with a junior hacksaw.

Get your 8" bars ready and fill the first hole with the anchor resin as per the instructions. Lock 2 stainless steel nuts at the end of the bar and screw the bar in with a socket or tap in with a hammer (dependent on resin instructions). Once the bar is into the masonry at least 4 inch remove 1 of the nuts and tighten the other 1 down so it is up to the wall.

Repeat the process for the other 5 and leave to set.

Add some washers to each bar so that together with the nut it will create a half inch gap between the joist and your wall. This will let any water running down your wall to continue its journey rather than ending up sitting on the joist and possibly soaking into your wall.

Fix 2 joist hangers to the joist, 1 either end approx 6" in. You can now fix the joist by fitting it on to the bars and securing with nuts and washers.

Fix your 2 posts for the other side at right angles to the ends of your joist using post spikes. The posts need to be 2" lower than the top of your joist.

Fix a joist to the top of the posts using one of the methods shown here. Sit your two 6x2 roof trusses in their joist hanger and rest the other end on the opposite joist. Mark the trusses where they sit on the joist and make a 2" deep on the marks. Use a chisel to knock out the wood and form a slot in each.

Place back into the hangers and knock the trusses down so the opposite joist is all the way into the slots. Make sure they are at right angles and check the levels. The trusses need to have a slight slope away from the home.

Once you are happy with the positions, nail into he hangers with galvanized nails and us a screw to fix the other side (screw from the top).

Your frame is now ready for a roof. We use 4x2 timber, overhanging a foot front and back and with slots cut in them so they sit on the 2 roof trusses.

You can also add a trellis to 1 or 2 sides to give privacy to a section of your patio.



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