1. Cool roof coating or paint
If your roof is of a suitable material, you can significantly improve its reflective qualities simply by applying a cool roof coating. Applied like paint, this coating helps roof surfaces reflect not only light but also thermal rays from the sun. It also helps make your roof more watertight and improves its working lifespan. The drawback of this solution is that it's not recommended for the ubiquitous asphalt shingle roofing. If you have metal or tile roofing, however, this is the solution for you. Metal roofs also take well to regular paint, so you can simply paint yours a light color rather than a dark color to improve its reflective powers.
2. Replacement materials
If you're on a budget, replacing your roof just to make it greener isn't an option. However, if you have asphalt shingles, you'll likely have to change the roofing in a few years anyway (since asphalt is one of the shorter-lived roofing materials). Switching to a more eco-friendly material when you do replace the roof is a good way to minimize extra expenditure while getting maximum greening power. Some eco-friendly roofs, such as slate, cost much more than a normal asphalt roof, but you can usually obtain a good-quality metal roofing for not much more than asphalt shingles. And because the metal lasts so much longer than asphalt, especially with a cool roof coating, it may even pay for itself before you have to replace it. Another low-budget way to go green during roof replacement is to send your old shingles to a recycling facility, keeping them out of the landfills and reducing the demand for new shingle production.
If you're not planning on replacing your roof for a few more years, you might want to think about what you can do in the meantime to be as energy-efficient as possible. One of the best ways to improve the efficiency of an asphalt shingle roof is by adding more insulation. Even if you already have adequate insulation, adding a bit more can help. This is because asphalt shingle roofs get so hot in summer that they tend to warm up the interior of your house a significant amount, making your AC system work harder. In fact, people who replace their conventional roofs with cool roofs may see a 20% decrease in their AC energy usage during the summer months, so the more you can insulate your roof to keep that heat out, the easier it will be on your AC unit.
These three options can help you if you want a more energy-efficient roof but don't have a lot of extra money. If you have a non-asphalt roof, you can just paint it with cool roof coating and you're all set. If you have an asphalt roof, try insulating it more until your next planned replacement, and then switch to a metal roof. Contact a company like K&R Roofing and Gutters for more information.