“We took a progressive approach to the crawlspace construction.”
When brothers Scott and Bryan Murray of Murray Engineering, a full-service engineering consultation firm based in Green Cove Springs, Florida, partnered to design and build Scott’s personal residence, they were not constrained by floodplain requirements. They still opted to build a raised wood floor. “The first reason was to add height to the structure and improve curb appeal, without having to utilize a bunch of fill dirt and being concerned about the settlement of that fill dirt. Second, I was looking for the wood-porch feel that is characteristic of the architecture that I like. Third was access to my mechanicals and electrical systems, and being able to maintain and upgrade those systems down the road. It’s a lot more feasible than on a slab,” said Scott Murray.
He wanted the house to have a traditional style but with a very modern use of building techniques and materials. “We’ve taken a home that you would typically see 100 years ago, similar to a farmhouse style with perimeter porches, and we’ve made it hurricane-resistant – to meet local code – and incorporated more progressive ideas on conditioning and properly managing moisture inside the house.”
The Murray brothers decided on an unventilated, enclosed and conditioned crawlspace, known as a closed crawlspace. “It’s my experience that, in our hot and humid climate, moisture is one of our biggest concerns,” Scott Murray says. “So we looked at how we control humidity and temperatures inside of the crawlspace. It just made sense to condition that area and keep it dry. That allows for all of the mechanical systems, the plumbing, electrical and the HVAC systems to be in a conditioned environment. It controls the odors in those areas. And obviously, if you don’t have moisture, you don’t have the mold growth.”
To achieve this, the Murrays took “a progressive approach to the crawlspace construction,” says Scott Murray. “We extended the first floor wall to the ground. Although my walls are 10 feet on the first floor, they are effectively 14 feet, because they extend approximately 4 feet from the finished floor to the grade level.”
All 14 feet of the walls are insulated. “Insulating all the way down to that ground level (instead of underneath the first floor) totally seals off the perimeter of that area, prohibiting outside air infiltration,” explains Scott Murray. “So we are dehumidifying that area. We are also conditioning that area and treating it as a living space.”
“I placed a 10-mil layer (of polyethylene) directly over the clean fill. It’s taped and seamed and turned up the wall. The poly and insulation help prevent moisture and air infiltration," says Scott Murray. "The poly also keeps pests out of the area. And (the floor) is elevated slightly above the exterior grade, so we don’t have any moisture buildup in that area.”
Scott also expects the closed crawlspace to result in energy savings. “Based on case studies I’ve seen, an unventilated closed system seems to use less energy (then a ventilated system) because there is no air infiltration from the exterior.”
According to Scott Murray, any builder can adopt the same progressive approach to crawlspace construction. “Learning these new techniques is not really rocket science. All you’re doing is closing the openings, putting in flashing around the perimeter walls, and preventing moisture from getting into the building envelope.”
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