Wet rot decay is very common in older buildings as timbers are often built into damp external walls. Any timbers with more than 20% moisture content will be susceptible to wet and/or dry rot decay. Dry rot decay is a particularly aggressive fungi attack and can travel through masonry. This is difficult to treat but some contractors use a Sovereign Solvaq FLX F1 Fungicide/insecticide treatment combined with a surface spray of exposed masonry with Sovereign Fungicidal Wall Solution Treatment which is effective. In conjunction with these treatments it is important to keep the moisture content of the construction below 20%. These treatments usually carry a thirty-year guarantee.