FOUNDATION PART 2: ROOF, ATTIC - Paperlessinspectors€¦ · Attic: Insulation UA Calculation If...

PART 2: ROOF, ATTIC & FOUNDATIONBuilding Science Review

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Building Science Review: Roof, Attic, Foundation

• This document will help you:• Recognize different types of roof construction & exterior finishes• Identify attic insulation type and quality• Distinguish between types of foundations.


Roof, Attic & Foundation: Roof• Four characteristics for roofs in Home Energy Scoring Tool:

1. Construction Type – 3 types:• Standard (most common)• With Radiant Barrier• With Rigid Foam Sheathing

2. Exterior Finish – 5 types:• Composition shingles (most common)• Wood shakes• Clay Tile• Concrete Tile • Tar and Gravel (flat roofs)

3. Insulation R-Value• R-0 to R-40

4. Roof Color – 6 options:• White• Light• Medium• Medium dark• Dark• Cool Color

Construction can be:1) Standard2) With Radiant Barrier3) With Rigid Foam Sheathing

A standard roof is most common. A roof with a radiant barrier or rigid foam sheathing can only be determined by looking at the underside of the roof from the attic.

A standard roof has no radiant barrier or foam insulation.


Roof: Construction – Standard Roof

A radiant barrier is a shiny silver foil or bubble wrap.

If the radiant barrier is not installed properly, the roof should be characterized as a “standard roof”.

Radiant barrier on the floor is an

improper installation

Exposed gable can negate the effectiveness of a

radiant barrier

Properly Installed Radiant Barriers


Roof: Construction - Radiant Barrier

Improperly Installed Radiant Barriers

Rigid Foam Sheathing is often white or pink, but may be other colors as well. The entire roof and gable ends must be covered with rigid foam sheathing in order to be considered valid and effective. Rigid foam sheathing may also be installed on top of the roof, under the exterior finish.


Roof: Construction - Rigid Foam Sheathing

If the attic is vented, any insulation installed at the roof is irrelevant and should be not be entered.

Composition shingles are the most popular roof type in U.S.


Roof: Exterior Finish – Composite Shingles


Roof: Exterior Finish – Wood Shakes


Roof: Exterior Finish – Clay Tile


Roof: Exterior Finish – Concrete Tile


Roof: Exterior Finish – Tar and Gravel

This category of exterior finish also includes roll and rubber membrane roofing.

The attic must be unvented, and the roof and any vertical surfaces between the ceiling and the roof that are exposed to the exterior must be insulated for the roof to be characterized as insulated.

If cathedral ceiling is chosen as the ceiling type the insulation level must be entered for the roof, not the attic (the input selection for attic insulation will be hidden).


Roof: Insulation Level

Color Description Example

White Smooth building material surfaces covered with a fresh or clean, stark white paint or coating.

Light Masonry, textured, rough wood, or gravel surfaces covered with a white paint or coating.

Medium Off-white, cream, buff, or other light-colored brick, bare metal, concrete block, or painted surfaces and white-chip marble-colored roofs.

Medium dark

Brown, red, or other dark colored-brick, concrete block, roofs with gravel, red tile, stone, or tan to brown shingles.

Dark Dark brown, dark green, or other very dark-colored painted, coated, or shingled surfaces.

Cool Color

Information from homeowner about roof reflectivity. Typically found only in hottest climates

Not obvious from observation.


Roof: Color

The attic requires 2 inputs. The first input, “Type”, has 3 choices:1) Unconditioned attic2) Conditioned attic3) Cathedral ceiling

Unconditioned Attic is the most common type of attic, and is characterized by exposed rafters and exterior venting. This area is sometimes used as storage space by the home’s occupants.

Conditioned attics are mechanically heated and/or cooled, and the walls, floor and ceiling are insulated and/or finished. Conditioned attics are often used as part of the living area of the house.

Cathedral ceilings are generally inaccessible, so it may not be possible to observe the insulation - in this case, the Assessor may need to make an educated guess based on the joist cavity size, local building practices, etc. Cathedral ceiling insulation must be entered in the roof “Insulation Level” field - when “Cathedral Ceiling” is selected in the Home Energy Score as the attic or ceiling type, the “Attic floor insulation” field will become hidden.


Roof, Attic & Foundation: Attic

1. Enter the R-Value for the attic floor insulation.

2. For cathedral ceilings use the Roof construction entries in the Roof section to provide the insulation R-value. Do not enter insulation values for both the attic and the roof.

3. If there are different R-values in multiple attic spaces, perform a UA calculation to determine the appropriate R-value to enter.

4. Batt insulation R-values should be derated based on current condition.


Attic: Floor Insulation

An unconditioned attic is defined by lack of HVAC supply registers or hydronic heating.

The picture to the right shows a typical unconditioned attic with insulation installed on the floor and exposed rafters or trusses supporting the roof.

This would be considered a fair installation because some of the insulation is compressed and edges are raised. If the high spots are not against the ceiling below, it is a poor installation.


Attic: Unconditioned

To be considered conditioned the attic must have at least one supply register or be opened to the conditioned area, and must be enclosed and insulated so it is isolated from the outside environment.


Attic: Conditioned

Use the Roof section when you have to characterize a cathedral ceiling.

The area of a cathedral ceiling must be calculated. The 4th tab of the Assessor Calculator can help with this.

If there are two ceiling/roof types, characterize them separately in the Scoring Tool.


Attic: Cathedral Ceiling

Batt insulation suffers more from poor installation than blown or rigid. Use the installation graphics and the derate calculator, along with your observations and measurements, to determine the proper insulation R-value.


Attic: Insulation R-Value / InchThese tables provide R-Value/Inch to correctly calculate insulation R-values.

Insulation in an attic may vary significantly as the image on the right shows. In this case the area around the hatch does not appear to be insulated at all; if that is the case, this uninsulated area has an R-value of 0.

You cannot simply average the insulation or R-values - a relatively small gap or hole in the insulated area has a significant impact on the entire insulation R-value. Think of it as being like an open window on chilly windy night. An attic that is 95% R-38, with a 5% gap of R-0, drops the overall value to R-13.


Attic: Insulation UA Calculation

If the insulation varies in depth or installation quality a special type of average calculation called a UA calculation must be made.

The best way to demonstrate a UA calculation is through an example: A house has two attic spaces. The first is an area (A) of 600 sq. ft. with R-11 insulation. The second is 350 sq ft and is insulated to R-38. Remember R = 1/U and U = 1/R. Average R-value is:R-11 = U₁= 0.091 and R-38 = U₂ = 0.026UA = 0.091 * 600 sq. ft. + 0.026 * 350 sq. ft.UA = 54.6 + 9.1 = 63.7U = 63.7 / (600 sq. ft. + 350 sq. ft.) = 0.067 R = 1/U = 1/0.067 = 14.9You can also calculate by dividing by the R-value rather than multiplying by U-value

We understand that no one actually likes to do these calculations by hand. If you are using the Sim, click the link below to download the Sim Calculator, which includes an insulation UA calculator. http://homeenergyscore3dtraining.com/course/hvacefficiency.php?id=3

Do not use the Sim Calculator for applications outside of the Sim - the Sim Calculator is for Sim training and testing only, and is inaccurate for other applications.

Contact [email protected] if you have questions.


Attic: Insulation UA Calculation

http://homeenergyscore3dtraining.com/course/hvacefficiency.php?id=3

mailto:[email protected]

Poor (badly compressed)

Use UA calculation to determine the R-value for the two areas combined

Fair - has gaps, but not compressed


Attic: Insulation Installation Quality

Good

Fair due to gaps - but not compressed


Attic: Insulation Installation Quality


Attic: Blown Cellulose Insulation


Attic: Blown Fiberglass Insulation


Attic: Rock Wool Insulation

Five types of foundations:

1. Slab-on-grade2. Unconditioned Basement

- no HVAC supply registers or radiators

3. Conditioned Basement- yes, HVAC supply registers or radiators

4. Unvented Crawlspace- no foundation vents or openings

5. Vented Crawlspace- foundation vents or open space

If the home has multiple foundation types, select the type that underlies the largest floor area and use those characteristics. If there are varying insulation amounts a UA calculation must be performed to determine the overall R-value.


Roof, Attic & Foundation: Foundation

If there’s no crawlspace or basement it’s almost always slab on grade. This is a poured concrete slab foundation that rests on the soil surface.

Insulation under the slab was uncommon until recently. If there is insulation it will be of a rigid type, R-5 in the input field. Insulation is especially found in warm climates and older houses (built prior to 2000 unless built to Energy Star standards). If you do not see it at ground level assume it is not there.

If the slab edge is insulated, you may be able to see foam type insulation along the transition from the foundation to to the exterior wall sheathing.


Foundation: Slab On Grade

Unconditioned basements do not have heating or cooling supplied directly to the space; i.e., there are no duct registers or radiators in the space. Just because they look finished doesn’t mean they are conditioned.If there is insulation in an unconditioned basement, it is typically fiberglass batts in the ceiling. Conditioned basements may have insulation on the walls. Most of the time, it is poorly installed. It may be falling from the joist spaces and there are often gaps and/or significant compression. Typically insulation in the joist spaces above basements and crawlspaces should be characterized as poorly installed.

The insulation may be behind drywall. If this is the case try to determine or estimate the thickness of the insulation based on the depth (stud size) of the wall.

If basement ceiling insulation is not installed directly against the floor above, derate the R-value to R-0. Insulation that is not installed directly against the surface that is meant to be insulating is ineffective.


Foundation: Unconditioned Basement

Conditioned basements have heating or cooling supplied directly to the space, i.e. there are duct registers or radiators supplying space conditioning. The walls may or may not be finished.

Insulation is standard in most conditioned basements in newer houses. Typically it will be fiberglass batts in the walls or a basement wall blanket, although other insulation materials may also be used.

The insulation may be behind the drywall. If this is the case try to determine or estimate the thickness of the insulation based on the depth (stud size) of the wall.

If insulation is not installed directly against the floor above, derate the R-value to R-0. Insulation that is not installed directly against the surface that is meant to be insulated is ineffective.

Unfinished but conditioned basement because of supply

duct registers.

Basement blanket


Foundation: Conditioned Basement

Unvented crawlspace is when a house is on a raised foundation with 3 inches to 4 feet of airspace under the floor. Unvented crawlspaces do not have open vents to the outside, and will usually be similar in temperature to the rest of the home. Any space over 4 feet is a basement.

If a home has a garage beneath conditioned space, then the garage should be considered unconditioned basement.

You must assess the insulation on the ceiling and walls of the crawlspace. If there is insulation in the joist space and on the foundation walls, enter the information about both.

It may be necessary to do UA calculation if the insulation is inconsistent across the ceiling or walls. If there is significant uninsulated space, like if much of the insulation has fallen, then measure the insulated and uninsulated parts separately.

Solid side walls in crawl space mean this is unvented.


Foundation: Unvented Crawlspace

A vented crawlspace is is the raised foundation under the floor that is open to the outside. The openings or vents in the foundation wall allow outside air to circulate into the crawlspace, so the air under the house is often a similar temperature to the outside air.

Houses on stilts or piers should be characterized as having a vented crawlspace.

The insulation on the ceiling must be assessed. Insulation on the foundation wall of a vented crawlspace should be disregarded as ineffective.

Note, it may be necessary to do UA calculation if the insulation is inconsistent across the ceiling.

Vents in the foundation wall

If insulation is not installed directly against the floor above, derate the R-value to R-0. When it is not installed directly against the surface that is meant to be insulated, it is ineffective.


Foundation: Vented Crawlspace

Example crawlspace or unconditioned basement insulation UA calculation

800 sq ft ceiling area75% is properly insulated with R-19 batts25% of the insulation has fallen to the crawlspace floor (use R-1 to avoid divide by zero error)

R 19 => U = 0.053R 1 => U = 1

600 x 0.053 = 31.58200 x 1 = 200(200 + 31.58) / 800 = 0.29R = 3.5

or divide by R-value since R = 1/U

600 / 19 = 31.58200 / 1 = 200(200 + 31.58) / 800 = .29R = 3.5


Foundation: Insulation UA Calculation

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