How to Prepare for Building an Arch or Pergola
The secret of a successful arch or pergola lies not only in a carefully planned design but also in sound construction. A well-made arch or pergola will look impressive and remain solid for many years if you do not cut corners. Always use good-quality tools and the right materials, and set aside enough time to do the job properly. You should be able to do most construction work yourself, although you may wish to employ a bricklayer to build brick posts.
Choose the Right Tools
If you plan to carry out much construction work, it is worth investing in your own set of good-quality tools. The tasks of setting out, groundwork, woodwork, and brickwork require a particular assortment of equipment. If you are planning only one project, then consider renting equipment. Most rental stores will carry the items required for the projects in this book. Make sure you have what you need before you start: stopping or improvising halfway through is inconvenient and even dangerous. Accurate measurements are also crucial to the success of your structure. Be sure to have on hand the necessities of a basic measuring kit: A measuring tape, wood block, string, builder's square, level and wooden pegs.
Before building, always look into local building codes and ordinances that apply to the type of construction you are planning. You may need to obtain a permit, and there may be fees. Contractors may also need to be involved.
Foundations and Footings
The spiked metal supports used in arch and pergola projects may be inadequate in areas where the soil freezes deeply. Check locally about minimum depths for foundations and footings.
Marking Out the Site
A good design will be spoiled by inaccurate setting out. Avoid the temptation to rush ahead, but take your time when measuring to make sure, first, that everything is square. Do not guesstimate the position of post holes: use a builder's square, string line, and wooden pegs to guarantee accuracy. Be consistent with which side of the pegs you measure from, either inside to inside or outside to outside. Always double-check measurements before starting to dig or cutting lengths of lumber.
- Check the diagonal measurements between corners to confirm post positions are correct.
- Allow at least 7ft (2.1m) head clearance between ground level and the underside of the overhead beams.
- Posts for taller pergolas should be a minimum of 4x4in (10x10cm) thick.
- Overhead crossbeams are usually about 6x2in (15x5cm) thick, with rafters of the same measurement or 4x2in (10x5cm).
When prepared, mark a site with two post positions, front and back on one side, with wooden pegs, builder's square, and string. Then, using the square and string, mark the position of the other two posts.
Once all four points have been set, check all the base measurements including the diagonals (which should be identical lengths) to confirm that everything is correctly set out.
As work progresses, develop the habit of checking measurements regularly with a measuring tape. Frequently confirm that posts are vertical and beams are horizontal, using a level. Avoid approximating or guessing measurements, and always double-check them before cutting out joints or permanently setting with screws or nails.
Rafters should be spaced out evenly on the overhead beams. Mark all the positions on both beams with a pencil. This is especially important if you are cutting notches yourself.
Use a level on the front and side of each spiked metal post support to check that they are driven into the ground vertically.