What is the minimum thickness for roof insulation?

8 to 10 Inches

Even in the case of cathedral ceilings, notoriously difficult to insulate, 2 by 12 rafters will allow sufficient space for ventilation, plus 10-inch batts of insulation, with at least R-30 value. In much of the southern U.S., R-30 is the minimum recommended insulation level for ceilings or attics.

How thick is insulation in roof?

Polyiso roof insulation is typically manufactured in incremental thicknesses from 0.5” to 4.5” with versatile options for meeting energy code requirements. Construction professionals should consult polyiso manufacturers for specific information regarding the relationship between product thickness and system R-values.

What is the minimum thickness for flat roof insulation?

What Insulation Thickness Do I Need for Flat Roofs? An uninsulated flat roof has a U-Value of around 1.5 W/m2K. When insulating one, you're aiming for a value of 0.25 W/m2K or less. To achieve this, you should insulate your flat roof with insulation boards totalling around 150mm thickness.

What R-value do I need for roof?

Install a single-ply roofing system

A single-ply roofing system (TPO or EPDM) has a 0.24-0.33 R-value with a typical installed thickness level, therefore you'll need considerable thickness of insulation to get you to an R-30.

What thickness of rigid insulation is used on flat roofs?

Closed-cell polyurethane spray foam will prove ideal for thermal insulation of a flat roof. Such an insulating solution involves applying several layers of PUR foam, with each layer around 1–2 cm thick. The effective roof insulation layer may range in thickness from 3 to 12 cm, as needed.

Why do you need roof insulation

What insulation is best for a flat roof?

Flat roof insulation is used to enable a room to feel warmer in the winter and cooler in the summer months. Wood fibre, cellular glass and polystyrene (EPS or XPS) all have good insulation properties, but foam works particularly well and is often found in modern constructions.

What type of insulation is used in a flat roof?

Roofing professionals emphasize that the choice of flat roof insulation should feature the appropriate R-value. The most expensive and highly recommended insulation is Polyisocyanurate (Polyiso) rigid foam. Extruded Polystyrene (XPS) is also an optimal choice, along with Expanded Polystyrene (EPS).

How thick should attic insulation be?

The recommended level for most attics is to insulate to R-38 or about 10 to 14 inches, depending on insulation type.

Is 50mm insulation enough for flat roof?

Xtratherm's comprehensive range of high performance flat and tapered roof insulation boards provide a guaranteed quality solution to flat roof specification. Xtratherm FR/TP should be fixed to a minimum of 50mm thick joists at 400mm (IRL)/600mm (UK) centres max with the plywood uppermost.

Is 50mm insulation enough for a warm roof?

You can use two sheets of 50mm but it is not enough to comply with current regulations. You will not achieve the correct "U Value" which is the thermal resistance. In a nutshell your roof could end up with condensation (interstitial). Ideally if using Celotex you need a minimum of 120mm.

How thick should insulation be between rafters?

Common rafter depths range from 100mm to 200mm. This limits the maximum thickness of the insulation between the rafters to between 50mm and 175mm. This generally would not be a sufficient thickness to achieve the U-values required to meet Building Regulations and more insulation would need to be added.

Is 2 inches of closed cell foam enough?

Closed cell spray foam should be 4- to 5- inches on the ceiling and 2- to 3-inches in the walls. This might come as a surprise to you, but honestly, this is all the spray foam it takes to get the biggest bang for your buck with the air seal and thermal resistance needed for certain areas of the home.

Can you put too much insulation in an attic?

It's possible to over-insulate an attic as too much will cause moisture buildup and eventually result in mold. Eventually, adding more insulation leads to diminishing returns in trapping heat as well.

What is the R-value of 2 inch Styrofoam?

With an R-value of 13.1 for a 2" thick sheet only two 2" sheets are required to achieve R-25. 2. Extruded polystyrene or XPS (foam is usually pink or blue) XPS has an R-value of 5 per inch of thickness requiring 5" of insulation to achieve R-25.

Does ceiling insulation need a vapor barrier?

Fiberglass Insulation

Like other batt-type insulation, fiberglass has a predictable R-value if not compressed but is difficult to fit around obstacles without leaving gaps. In most climates, it needs a vapor barrier.

Can I insulate the underside of my roof?

Open-cell spray polyurethane foam or closed-cell spray polyurethane foam (ccSPF) insulation can be sprayed along the underside of the roof sheathing to provide a conditioned and insulated attic space that can be durable and efficient in all climate zones (see Figure 1).

Is it OK to insulate roof rafters?

Insulating between rafters will do no good, because the attic should be ventilated, and the rafter insulation would be between two unheated spaces. You can add insulation to the floor; the more the merrier. Just don't put it in the eaves. Also, make sure the attic is well ventilated.

Is R 30 insulation Good for attic?

The average recommended level is 14 inches of R49. In Zone 2, the average minimum requirement for attic insulation is 9 inches of R30 fill. The average recommended level is 17 inches of R60. In Zone 3, the average minimum requirement for attic insulation is 9 inches of R30 fill.

What kind of insulation do you use for attic rafters?

R30 in hot climates (like California) R38 in temperate climates (this is typically the desired level for residences in California)

Should a flat roof have insulation?

A flat roof should have a layer of insulation built into the structure at some level. When an insulated roof is built from new, the insulation layer can be included at different levels within the structure.

Can you insulate on top of a roof?

Insulated roof assemblies can be vented or unvented. There are lots of different ways to insulate this type of roof, but one of the best methods calls for the installation of rigid foam insulation above the roof sheathing.

How do you install insulation under a flat roof?