It provides a solid flat surface to attach the new metal roof to.
Roof purlin metal building air gap.
Metal roofing ridge cap is the trim placed along the roof s ridge the peak where two roof slopes meet up.
This gap allows some vertical eave to ridge movement of air between the purlins and the metal roof.
In other words it s put on last the cap to the job.
They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top.
So i ll start by saying something that might sound controversial but really isn t.
Most ridge cap comes in pieces 10 6 long.
Metal roof purlins are installed horizontally under metal roofs.
A ridge cap is normally installed only after all metal roof panels and any other trim are in place.
A vented attic where insulation is placed on an air sealed attic floor is one of the most underappreciated building assemblies that we have in the history of building science.
Ventilation air follows exactly the opposite path.
Purlins at a 45 degree angle still provide sufficient support for installation of the metal roof panels.
They give added support to the roof and also provide a nailing surface for the end panels and drip edge.
Metal roof coatings with solar reflectance can help building owners save substantially in annual cooling costs.
Installing the metal roofing over 1 4 s allows the ability to also install additional insulation under the metal roof that can t be done the other two ways.
Research has confirmed that creating an air space under a metal roofing system will increase energy savings during both summer and winter months.
So much information has been devoted to the subject of roof venting that it s easy to become confused and to lose focus.
But probably the best benefit that comes from using purlins is the air gap it creates between the metal roof and the existing shingle roof.
It creates an air gap between the back of the metal and the shingle roof which allows for airflow.
The metal will be attached to at least 3 4 purlin and 1 2 plywood instead of just 1 2 plywood which should make the overall roofing system stronger.
Rising along the underside of the angled purlin until it reaches a gap then rising up to the next purlin and so on to exit at the ridge or gable.
Purlins are 2 by 4 feet and are installed much like metal roofing.
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