# U-Factor vs. R-Value

The U-factor and R-value are both measures how much heat (or cold) can pass through a given piece of a building such as a window, wall or floor.  The U-factor is the original measurement taken and is used to calculate the R-value.  Let me explain…

The U-factor represents how much heat or cold can pass through an object so the higher the U-factor the worse the object (such as a window) is at insulating while the R-value represents how good the object is at insulating so the higher the R-value the better the object is at insulating.

The R-value is calculated using the U-factor’s reciprocal value.  A reciprocal value is when you take a fraction and flip it.  For example, a U-factor of 0.35 = 35/100 so it’s reciprocal R-value would be 100/35 = 2.9.

The R-value is a better presentation of the data than the U-factor because it increases with the quality of the window and the values are not small fractions.  For this reason the R-value is used most often in labeling for windows, etc.

Reference: p. 33 “U-Factor and R-Value: What’s the Difference?” Journal of Light Construction, Vol. 31

# A Lesson on Insulation

Earlier we covered the topic of ice dams.  The culprit of many ice dams can be poor insulation in the attic.  Now that the warm weather is on its way it may seem this problem can wait another season but poor insulation can also mean a hotter house on warm days.  The question now arises: how do I best insulate my attic?  There are many different ways this can be done.  Below is a list of popular insulation materials.  Usually a combination of insulation types is used in a home.

 Type Material Appearance Pros Cons Fiberglass Glass Fibrous wool / cotton candy.  Can be pink, yellow, or white, depending on manufacturer. Easy to install, inexpensive Dangerous to breathe (wear a mask when installing), heat and moisture compromise quality, mice will nest in it. Rockwool (new version) Minerals Grey wool blanket Easy to install, more airtight, safe to install by heat sources, can get wet, nontoxic environmentally friendly material More expensive than fiberglass insulation (10% or more) Foam Board Polyurethane Foam boards that can be blue, grey, or pink depending on manufacturer. Easy to install where appropriate. Rigid insulation is not appropriate for every part of the home. Blown Insulation Made out of various materials including cellulous, fiberglass, and minerals White fluff Spreads evenly, fills in between outlets, wires, pipes and ductwork, and eliminates gaps in insulation.  Good for attic floor. Need professional with equipment to install. BIB (Blown in Blanket) Fiberglass, fabric White fluff held in place by fabric sheets. Fills space between studs very well. Need professional with special equipment to install. Spray Foam (Open Cell) Chemical combination. Made up of broken, unclosed bubbles.  Soft consistency Shaving cream Inexpensive, fills space well, water can pass through (can be con if you want it to block water) Need professional to install, R-Value is very good, but closed cell is better (see below) Spray Foam(Closed Cell) Chemical combinationMade up of dense, closed bubbles.  Denser, harder consistency. Shaving cream High R value, water and air cannot pass through Need professional to install, more expensive than open cell

Fiberglass Insulation

When looking at insulation you are going to see a lot of talk about “R-Value”.  According to EnergyStar.gov, R-Value is “a measure of insulation’s ability to resist heat traveling through it.”  The higher the R-Value the more effective the insulation.  A chart on the same website shows homes in Maine to require insulation with an R-Value of 49-60 for the attic walls and 30-60 for the floor, depending on the current amount of insulation in the attic.

http://howtohomeinsulation.com/insulation_basics_types_insulation.html

http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

# Ice Dams

Now that the first snow storm has hit (or second if you count the one in October..), it is time to think about winter maintenance.

One common problem this time of year is ice dams. An ice dam is when melted water freezes at the roof overhang causing a build up of water and ice on the roof.  The water that is no longer able to drain can become a leak in your ceiling.  Besides the ceiling, your roof risks being damaged by the ice and moisture.

Ice dams can be caused by poor insulation.  If too much heat is escaping from the attic, the snow on the roof can melt and flow down to the overhang where it refreezes.  You might think that it is your roof that needs to be repaired when, in fact, it is your home’s insulation that needs to be improved.  Frozen and clogged gutters also do not help and keeping them clear of debris and ice can help.  Finally, keeping the roof clear of heavy snow build up can help as well.

ice dam diagram

The Energy Star website has some excellent tips for preventing ice dams here.

# Word of the Week Quiz Answer: Stringer

Last week I asked for the definition of a stringer in reference to building. We had some creative answers (neither of which were correct, but fun to read!):

“Stringer= the tool used to hold fish caught by a construction worker when they should otherwise be constructive.”  M.D.

“..a guy who walks back and forth in font of the company, saying: wanna build a home?- to passers -by.” I.V.

A stringer is the wood that acts as the support in various structures including walls, floors and stairs.  In the case of floors, the stringers are the boards that make up the structure under the floor boards.

The stringer for steps are cut into the shape of stairs.  There are 2, sometimes 3, stringers supporting a set of steps.  When you look at steps from the side, you can see the stringer.

The illustration is a doodle a stair stringer.

# Word of the Week QUIZ

For the past several months we have been defining different building terms to help you learn the anatomy of your home. This week we want to test your knowledge of building and architecture!

The quiz word for this week is fenestration.  If you know the definition of fenestration in the context of construction, please post your answer below.

# Builder Vocabulary: Screw Head Styles

Depending on the task at hand and the tools available, there are different styles of screws to choose from.

First there is the slotted vs. the Phillips head. A slotted screw head is used with a flat-head screwdriver (a.k.a slotted-tipped, straight-tipped, flat-blade, etc.) A slotted screw has one groove going straight across the head for the screwdriver’s tip to fit into. (1)

A Phillips screw head has a plus-sign shaped groove made to fit a Phillips tip screwdriver. The Phillips tip screwdriver is a fairly new screw from the 1930’s designed to prevent over torqueing. It did this by the shape of the grooves which caused the tip of the screwdriver to slip out before too much torque is applied. The screw is also easier to screw in and less force is needed embed the screw. (2)

Besides the two basic grooves, there are many different shapes the screw head can take including flat, round, oval, pan, truss, fillister, and hex. The shape used depends on the project.

1. Builder’s Comprehensive Dictionary (Robert Putnam, Reston Pub. Co., c1984) p.370

## Words of the Week: Arbors, Trellises and Pergolas

### Image

Let’s define these visually.

This is an arbor (an outdoor archway):

An arbor built by Chris Ryan

This arbor was built by Handyman Project Manager Chris Ryan for a customer.

This is an arbor with a trellis (latticework to support climbing plants):

Arbor with Trellis by Randy Boyer

Pergola style Roof on Randy's Arbor

The pictured arbor was built by Project Manager Randy Boyer for his garden.  The top of this arbor is very much like pergola…

There are also pergolas which are posts with a simple roof structure:

Pergola built by Duane Overlock

This pergola was built by Foreman Duane Overlock for a customer.

This is the entrance of the customer’s home which has a mock pergola:

Pergola style entrance

# Word of the Week: Cribbing

A lightweight crib structure. Picture by Bill Bradley: http://www.builderbill-diy-help.com/

Cribbing is used when the structure needs to be jacked up from its foundation. Cribbing involves building a crib of wood timbers in a Jenga type formation in key spots underneath the building. The cribs will provide support to keep the building up when it is lifted from its supporting columns.

Cribbing is also used for mining and landscaping.

1. Builder’s Comprehensive Dictionary (Robert Putnam, Reston Pub. Co., c1984) p.100, p.171