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

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.

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

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.

Here’s an easy one: What is a Stringer (in reference to home construction)? Post your answer online!

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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.

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

2. http://www.wisegeek.com/what-is-the-difference-between-a-flathead-and-phillips-screwdriver.htm

3. http://www.engineeredpartsinc.com/head-types.htm

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