We have renovated an ancient house here in France and I guess many of you are in the same situation. There are two reasons why I think I have some experiences that are valuable to share with others. The first reason is that I have done a lot of mistakes that you should not have to do. The second is that I, being a retired university professor in architecture, have the ability to reflect on my mistakes and learn from them. I might also have some abilities to communicate my know-how to others who are in the same situation.

The latest project I did and that rewarded me with a serious attack of lumbago was a pergola on the roof terrace. The reason we wanted to have a pergola is that I want the shade – my wife does not – but we both want a more sheltered place for our dinners and breakfasts. My wife has always dreamt of having some climbing plants and we don’t have a garden – thanks good - so a pergola was of great need.

The first thing you have to decide is the design of the pergola. I choose a standard construction that I like best. The difficult thing is however to decide the dimensions of the construction. The eye will easily fool you. If you go strictly on construction principles it tends to be to thin and it will not look nice. If you on the other hand want to be on the safe side you tend to make the construction too heavy and that is not good either. You like a pergola to look light but not spindly and when the plants start to grow they add some visual weight to the construction.

So I decided on a construction with two primary beams with the dimension 100x40 mm. The length was approximately 2.5 meters. On top of these I put three secondary beams with the same dimension and approximately 3 m long. The actual “roof” of the pergola was 2.5 m long planks with the dimension 100x25 mm with a distance between them of 200 mm.

Three layers of construction would be quite thick however if I had just put them on top of each other so I let the top beam always cut into the lower one 40 mm. In this way I could reduce the construction height from 300 mm to 220 mm which made it quite nice. I only needed 1 pillar and I found that 100x100 mm is a good looking dimension. Remember not to let the pillars have direct contact with the ground or the floor. It will draw water and by the time rot, but there are constructions that allow a distance between the supporting floor and the end of the pillar.

The second important decision is what wood to use. I decided on red cedar. In the French climate this wood is very good as it resist water and do not rot and it also contains chemical substances that different bugs that eat wood do not like. You do not even have to treat it. It is light, which is good if you have a bad back, it is very easy to work with and it looks beautiful. It is however poisonous so be careful when you work with it. Use gloves, do not get dust into you eyes of breath it in and be careful not to get splinters in your hands. It is allergenic to many people and I noticed my hands got very funny after a while. Off course I read about the hazards too late to benefit from the knowledge.

Another thing you have to know is that the wood is corrosive so you need to use stainless steel screws and nails and at least galvanized fixtures if you think stainless is too expensive – which it is.

A piece of advise when you cut the beams to fit into the lower one – cut the top beam, not the lower as that will cause pockets for water to get into. Also put the beams on place and mark where to cut in place. If you cut the beams by measuring where the cuttings should be they will not fit. It is easy to do these cuttings – just make two parallel cuts with a sharp saw to the depth you need (in this case 40 mm) and give it a blow with the hammer. The bit just pops away as the cedar wood is very even in its structure. Even the bottom of the cut a little with a rasp. If the dimensions are a little too thick to just pop off, use a chisel and take it a way bit by bit.