Attic Insulation Rafters Or Joists

Insulating attic floors unfinished or uninsulated attics need a layer of protection against air migration.

Attic insulation rafters or joists.

Install batting between the attic s floor joists. The ceiling joist system is typically constructed from substantial two by tens or larger dimension boards but some older homes have smaller joists. They are nominally 2 inches thick actual width usually 1 1 2 inches and come in a variety of widths from 8 to 12 inches. Polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials.

In practical terms you can choose between mineral wool or insulation boards. Unless expressly built so an attic s joists are meant for carrying the load of the ceiling below and related elements collectively known as the dead load. Joists are traditionally made from timber. So insulating the floor of the attic is not only the best solution but it is also the simplest and cheapest.

In finished attic rooms with or without dormer insulate 2a between the studs of knee walls 2b between the studs and rafters of exterior walls and roof 2c and ceilings with cold spaces above. Hire a pro to install spray foam insulation. If you want to install standard r 38 insulation. 2d extend insulation into joist space to reduce air flows.

If you decide on mineral wool such as glass wool or rock wool you will need to put down a damp proof membrane. If you re considering turning your attic into conditioned storage or living space it s worth changing tactics to insulate between the rafters and wall joists instead of the floor. You can use rigid foam panels or do as tom silva does with nearly all houses these days. Even rafter insulation can encourage damp as it stops draughts and reduces natural ventilation.

Insulation between the joists will make your attic much colder so this could worsen your damp problem. Standard joist spacing for the installation of attic flooring materials is 16 inches on center oc meaning the distance from the center of one joist to the center of the next joist is 16 inches. The ceiling load may include items like drywall ducts recessed lights bathroom fans and attic insulation.