The following thoughts and guidelines are based on my experience.
Firstly, you have to consider the requirements you have for an arena. The main considerations are: Is your arena mostly for jumping or flatwork, or maybe lungeing. How much use will it have, what is your budget and what space have you available for the arena. Also look ahead, because your arena will hopefully have many years of use, so consider whether your needs will have changed in 10-15 years time.
Size. Construct the biggest size you can afford. In event or dressage competitions, you will be riding in either a standard size 20m x 40m arena or an international size 20m x 60m. Even some prelim tests are ridden in a 20m x 60m arena. If you do more jumping than dressage, consider a wider width, such as 25m and then have the longest length you can afford, if possible, 40m minimum. The smallest size you could use is 20m x 20m, which would allow you to walk trot and canter a balanced horse, but larger is advisable. It can be difficult to keep a horse straight if you are constantly riding in this small an area.
Surface: Again, go for the best surface you can afford. Many people regret trying to save money putting down a cheap surface and end up replacing it a few years later which is false economy. Ride on as many surfaces as you can. Talk to people who have surfaces themselves or who have lots of experience re different surfaces available. Phone up as many arena manufacturers as you can and discuss your requirements, you can learn a huge amount by talking to them. Many of the arena manufacturers have lists of people in your area who have used them to construct an arena and you can contact them to find out how happy they are with their surface.
I needed a surface which was hard wearing in all weathers and suitable for jumping and flatwork, with pretty much continuous use ever day. My budget was limited, but equally, it was not an option to put down a surface which might be slippery, hard, deep, or dusty. I chose a mid priced option of putting down a very good quality silica sand with rubber on top. Therefore it would give grip and spring and never get too deep, dusty, nor hard.
Where will you put your arena? The best naturally draining ground you can find on your premises with easy access from your stables. Also consider the big lorries and diggers which will need access during the construction period. If it is at all wet when your arena is built, the vehicles will make a LOT of mess and the lorries may not be able to access the area at all if it is too wet and muddy. The required planning permission mentioned below, may also have a bearing on where you are able to place your arena.
Planning permission Yes, you do need planning permission to construct an outdoor school. Contact your local council.
So, who will do the work. Either the work will be done by a dedicated arena manufacturer, or you may choose to do it yourself if you have the equipment and expertise available to do much of it yourself. (eg. those who live on a farm). However, if you do the work, there will be no guarantee – only yourself to blame if anything goes wrong! I used a local contractor with a digger to do much of my work (he was recommended to me having done a very good arena nearby) and the guys on the farm helped too. However, it was quite a stressful time and I was unable to do any work for 3 weeks while overseeing the construction, so next time, I will pay the extra and have it done for me – less stress, less call on my time and a nice guarantee to go with it – usually 5 years.
The arena. The ground must be levelled, but a very slight fall in the level is advisable. Boarding was placed round the outer edge of my arena and upright posts were placed ready for the rails, leaving a riding area of 20m x 60m. My arena (20m x 60m) has 6 herringbone drains, filled with perforated piping and stone and leading to one long drain which extends down the entire length of the arena and out to a soakaway which was dug outside the arena. The whole arena was then covered with a membrane, before placing a layer of stone on top. A second membrane was then placed on top of the stone with all overlapping edges stapled for added security and to help prevent movement and tearing of the membrane. On top of this membrane was placed 4.5 inchs of silica sand, very carefully levelled to ensure an even depth and then rolled in as much as possible. 2 inches of rubber was then put on top.
Watering in. It is very important that silica sand is very well watered in before you ride on it. Think of dry sand on a beach which never gets the sea on it and how deep it is and how difficult it is to walk on. Compare the feel of sand after the tide has gone out – that sand is solid under your feet. That is how you want your silica sand to be – almost inpenetrable. The rubber then sits on top and holds the moisture in the sand, protecting it from the sun drying it out. Of course, when we have really hot and dry spells, there is some drying out of the top of the surface, but if you scrape down a few inches, the sand will or should still be damp and compact. Ideally, your arena needs a few days of constant rain on it to settle it in. Dont be in a rush to ride on it. Test how firm the sands feels with your finger – it should be almost impossible to push your finger through the sand.
Maintenance is essential. The more you maintain your arena, the longer it will last. Lack of maintenance is likely to cause damage to any membrane under your surface. If you can afford an arena leveller to tow behind your 4×4 vehicle or quad bike, that will help a great deal, but you will still need to do some handwork with a rake round the track, to pull in the surface which gets kicked out. It is also advisable to pick up droppings and it will make your lovely new and probably relatively expensive arena look nicer too. If droppings are left, they will get mixed in with the surface and then if it rains, bits will get washed through the surface and can eventually clog up the membrane.
Conclusion: You will wonder how you ever coped before you had an arena. Your horses will improve, your riding will improve and your competition results will be better. It is also likely your horses will stay sound for longer as they are being ridden on a level and consistantly ‘giving’ surface. But remember also, that constantly schooling your horse can cause wear and tear to his joints and dont forget that he also needs a change of scenery to prevent boredom and staleness creeping in.
The comments above are based on my experiences and are not a complete guide to building an arena. There are many factors to be considered and I strongly advise that expert advice is sought. I spoke to many many people before making my final decisions on how to do my own arena. A great place to do research is at Badminton Horse Trials where many of the leading arena manufacturers will have stands. They also include samples of their surfaces on their display stands.