However, total value sales were 3.5% up in August compared with the same month last year.
Two categories did better – timber and joinery products (+9.5%) and landscaping (+6.9%).
Heavy building materials (+1.6%) and plumbing heating and electrical (+1.2%) were among six categories that grew more slowly, while four categories sold less this year.
The first eight months of 2018 were 4.5% ahead of the same period in 2017, with one additional trading day this year. Plumbing heating and electrical (+9.2%) did best, with timber and joinery products (+7.3%) also strong. Landscaping (+3.9%) and heavy building materials (+3.3%) were among nine categories that grew more slowly.
Average sales a day for January to August, which takes the difference in trading days into account, were up 3.9% on the same months last year.
The rolling 12 months of September 2017 to August 2018 were 4.8% above the same 12 months a year earlier. Plumbing heating and electrical (+8.7%) was strongest, followed by timber and joinery products (+6.9%). All categories sold more.
The Builders Merchant Building Index (BMBI) tracks builders merchants’ actual sales to builders and contractors using GfK’s Builders Merchant Point of Sale Tracking Data. The BMBI represents over 80% of the value of the builders merchants market.