TABLE OF COSTS BEHIND FEMA P-1100

            TABLE OF COSTS BEHIND FEMA P-1100

FEMA P-1100 has been codified into ICC 1300, a-yet-to-be-published guideline by The International Existing Building Code.  This particular study was written with a view to help contractors decide if they want to keep using the universally accepted retrofit standard called Standard Plan A or the new guideline FEMA P-1100. 

The Standard Plan A retrofits describe here do not use the table found in Standard Plan A. Rather, they use the actual, current, and much higher values for bolts, framing anchors and plywood. For example: the original Standard Plan A 4″ o.c. 8d rated sheathing has a capacity of 380lbs. The Standard Plan A retrofits shown here use an upgraded 8d nails 3″ o.c. 550lb plf in structural 1 plywood. The same engineering goal is met is found here but the cost is reduced because these higher hardware and plywood values are used. A comparison of the original archaic values in Standard Plan A and the actual values are described here. The pricing for hardware and plywood throughout this comparison uses the standard pricing used by Bay Area Retrofit Inc and is listed below. You may want to start by watching these videos on Standard Plan A which look at its many flaws, though its flaws are nothing compared to FEMA P-1100.

 

 

Comparison Between Single Story Standard Plan A And FEMA p-1100

Here a FEMA p-1100 retrofit is compared to a Standard Plan A retrofit for the same 1350 Square Foot 1-Story Light Construction House

1350 Square Foot Light Construction House in ICC 1300

$16,080.00

1350 Square Foot Light Construction Standard Plan A Design Cost Compared To ICC 1300

$5,622.00

Is The Engineering Rational in FEMA P-1100?  

The earthquake resistance of each component, i.e., the bolts, plywood, and L90s, should be more or less equal to create a balanced and money saving retrofit. The thinking behind this is that a retrofit is only as strong as its weakest connection. The plywood, bolts, and L90s work as a system. If one component fails the entire system fails. For example, in the FEMA P-1100 retrofit above the L90s can resist 18,000 lbs  of force on each wall line, the plywood 9,120 Lbs, and the bolts 23,125 lbs.  The retrofit will fail as soon as it must resist 9,120 lbs. of force provided by the plywood; anything over that in the L90s and plywood  earthquake resistance is redundant and a waste of money.  In this case  all 4 wall lines total 56,020 lbs. of excess bolts ($2,875.00) and 35,120 lbs. of excess L90s ($1,480.00).  This exceed hardware translates into $4,355.00 of excess cost.   Here is a 3:40 video that explains how balanced retrofits work.

 

A 1350 Square Foot 1-Story Medium Construction Comparison

 ICC 1300 Design Of 1350 Square Foot Medium Construction Compared To Standard Plan A

$17,784.00

 

 Standard Plan A Design Of 1350 Square Foot Medium Construction Compared To ICC 1300

$6,644.00

These two figures compare an FEMA P-1100 retrofit (on the left) with a Standard Plan A retrofit (on the right) for a medium construction 1,350 square foot house. A Standard Plan A retrofit will cost $6,644, compared to $17,784 for a FEMA P-1100 retrofit. Notice how grossly out of balance the FEMA P-1100 retrofit is. The 21,000 lbs. of bolt capacity in p-1100 exceeds the 11,760 lb. plywood capacity by 9,240 lbs on each wall line for a total of $4,320.00 excess cost when the excess on all four wall lines are added together. We also find 15,065 lbs. of excess  L90 capacity on each wall line (60.260 lbs. when all four wall lines are added together) for a total of 65 excess L90s  ($3,198). These excess bolts and L90s cause this P-1100 retrofit to be far more expensive than it needs to be.

On the other hand, the Standard Plan A retrofit is balanced with 6,600 lbs. of plywood, 6,000 lbs. worth or bolts, and 6,475 lbs. of L90s on each side. This balanced Standard Plan A retrofit costs considerably less because it is balanced.

A 1350 Square Foot 1-Story Heavy Construction Comparison.

 ICC 1300 Design Of 1350 Square Foot Heavy Construction House.

$19,592.00

Marked Cost Reduction In Standard Plan A Compared To ICC 1300

$7,342.00

Again, notice how grossly out of balance the FEMA P-1100 retrofit is.

Comparing FEAM P-1100 and Standard Plan A 2-story Retrofits

FEMA P-1100 two story retrofits use the same EARTHQUAKE RETROFIT SCHEDULE as 1-story houses. The only difference is that these retrofits often use holdowns, (called tie-downs in the table), which resist overturning forces.

A 3150 Square Foot 2-Story Light Construction Comparison

Applying the same thinking process we used in evaluating 1-story houses shown below, we see the FEMA P-1100 retrofit on the left will cost $49,384, compared to a $9,158 Standard Plan A retrofit shown on the right. 

Again, notice how grossly out of balance the FEMA P-1100 retrofit is where the capacity of the plywood is 18,240 lbs., the bolts almost twice that amount at 18,240 lbs., and the L90s almost three times that amount at 44,000 lbs. All of this excess increases costs immeasurably. 

Compare this to the almost perfectly balanced Standard Plan A retrofit with 8,800 lbs. of plywood, 9,000 lbs. worth or bolts, and 9,250 lbs. worth of L90s on each wall line.

Notice how the available foundation on the P-1100 retrofit is less than the linear footage of plywood required by FEMA P-1100. In my experience with designing seismic retrofits for two story houses, which are invariably rectangular, I cannot think of a single instance where P-1100 will work on a two story house.   This will be the case even if the house is a perfect square. 

IMAGE OF TWO STORY ICC 1300 RETROFIT DESIGN THAT IS IMPOSSIBLE TO INSTALL.

$49,384.00

CHEAP TO INSTALL TWO STORY STANDARD PLAN A RETROFIT COMPARED TO EXPENSIVE 3150 SQUARE FOOT ICC 1300 RETROFIT.

$9,158.00

3150 Square Foot 2-Story Medium Construction Comparison

Assuming 2-story houses where FEMA P-1100 will work actually exist, when we apply the same thinking process used for 1-story houses to this house we discover that this FEMA P-1100 retrofit will cost $47,284 compared to a $22,530 Standard Plan A retrofit. The same problem with balance applies here. Notice how the Standard Plan A retrofit is almost perfectly balanced.

EXPENSIVE AND IMPOSSIBLE TO BUILD ICC-1300 RETROFIT 3150 SQUARE FOOT MEDIUM CONSTRUCTION

$47,284.00

AFFORDABLE STANDARD PLAN A RETROFIT OF 3150 SQUARE FOOT MEDIUM CONSTRUCTION HOUSE COMPARED TO ICC 1300

$22,530.00

3150 Square Foot 2-Story Heavy Construction Comparison

When we apply the same thinking process to this house we discover that the FEMA P-1100 retrofit will cost $55,276 compared to a $24,392 Standard Plan A retrofit. The same problem with balance applies here.

SAMPLE TWO STORY FEMA P-1100 RETROFIT 3150 SQUARE FOOT HEAVY CONSTRUCTION

$55,276.00

COMPARISON SAMPLE TWO STORY STANDARD PLAN A RETROFIT 3150 SQUARE FOOT HEAVY CONSTRUCTION AND FEMA P-1100

$15,840.00

No Cripple Wall Retrofits

Here we compare a 2-story 3,150 square foot medium construction FEAM P-1100 retrofit of a house without cripple walls. In this retrofit we are using the Type B Connector (the brand name is the Simpson Strongtie FRFP) from the EARTHQUAKE RETROFIT SCHEDULE which is  FEMA P-1100 approach and compare it to a 3,150 square foot 2-story Standard Plan A retrofit no cripple wall retrofit (on the right) which uses the Simpson StrongTie URFP. The FEMA P-1100 retrofit will cost $42,793, compared to a $6,438 Standard Plan A retrofit.

SIMPSON STRONGTIE FRFP TWO STORY P-1100 RETROFIT 3150 SQUARE FOOT MEDIUM CONSTRUCTION

$43,793.00

SIMPSON STRONGTIE URFP TWO STORY SIMPSON P-1100 RETROFIT 3150 SQUARE FOOT MEDIUM CONSTRUCTION

$6,438.00


In this last part of our study we look at what happens when a FEMA P-1100 construction detail seen on the lower right is applied to a medium construction 1,350 square foot single story house. A construction detail is a drawing that shows a contractor how to build something.

The dark and light blue lines in the detail are 4 foot long shims called “runners”. The red lines are Type B Connectors (Simpson FRFPs). This is another case where the linear footage of foundation is not long enough for the length of the plywood required by the EARTHQUAKE RETROFIT SCHEDULE. The detail has many other problems, including a building code violation. This is fully described in this video.

ABSURD CONSEQUENCE OF FEMA P-1100 RETROFIT USING ITS CONSTRUCTION DETAIL

ICC 1300 TYPE H CONNECTOR DIAGRAM


How This Study Was  Done

The most effective way to conduct this study was to apply the two guidelines to an identical house where the existing construction materials, square footage, and weight of the house are the same.

Throughout this study the pricing per piece of hardware and price per linear foot of plywood is based on Bay Area Retrofit’s current price schedule shown below.

 

Pricing  
5/8” Bolts $77 each
URFP $135 each
FRFP $135 each
L90 $39 each
Plywood <  4 feet $90 plf
Plywood >  4 feet $165 plf
Tie Downs $215 each

                        

The Earthquake Resistance of Plywood and Hardware

The table below contains the earthquake resistance of the plywood and hardware used in this study.  These values are derived from APA Research Report 154, the National Design Specification, and the Simpson StrongTie Catalog. 

Capacities  
5/8” Bolts in 2” Close Grain Redwood 1500#
URFP 1530#
FRFP   960#
L90 925#
ICC Light Construction Rated Plywood 380plf
ICC Medium Construction Rated Plywood 490plf
Standard Plan A comparison 3” o.c. Structural 1 Plywood 550plf
Heavy Construction Rated Plywood 640plf
     

House Weights

House weights along with the base shear formula tell us how much hardware and plywood we will need.  Mr. Jim Russel P.E. figured out precisely how much hardware and plywood will be needed by using a simple formula described in these videos.   These are the weights he used depending on how the house was built.

These Are the Weights In Standard Plan A Per Square Foot And Category.  I do not know the weights used in FEMA P-1100

Shingle roof, wood siding, and sheet rock inside.  This is light construction

 One Story

 34# per square foot

Two Story

29.5# square foot

 

Shingle roofing, wood siding, and plaster inside.   This is medium construction

One Story

45# per square foot

Two Story

41# per square foot

 

Shingle roofing, stucco exterior, and sheet rock inside.   This is also medium construction

 One Story

41# per square foot

Two Story

36.5# per square foot

 

Shingle roofing, stucco exterior, and plaster inside.  This is heavy construction

One Story

 50# per square foot

Two Story

45# per square foot

House weights used in FEMA P-1100 are unknown. 

 

FEMA P-1100 was created by a group of  wood scientist and engineers using $22,400,000 in FEMA funded research grants, both directly and indirectly starting with the CUREE Woodframe Project.  So far as the author can tell, its damage forecast damage scenarios are based on computer modelling and engineering theory as well as various lab tests and reports.  A list of these 21 lab tests and reports can be seen here.