3.3 ESTIMATING

Calculating Block, Concrete & Rebar

The following pages contain information on estimating block, concrete and rebar. An example plan with calculations can be found at the end of this section.

Estimating 6 and 8 inch Core
Fixed-Web Block

Ln	Objective/Outcome	Operation	Ln Ref	Calculations
1*	Perimeter	ADD all sides
1a*	Find Wall Height	SEE PLANS
2	Buildings wall sq ft	MULTIPLY Perimeter by Height	Ln 1 x 1a
3	Gross Blocks	DIVIDE Bldg wall sq ft by 4.0	Ln 2 ÷ 4.0
4	Square Footage of Openings	Check plans and/or Window / door schedule
5	Total Square Footage of all Openings	ADD windows & doors sq ft to obtain total sq ft	Line 4
6	Openings - Block reduction	DIVIDE Total Openings sq ft by 4.0	Ln 5 ÷ 4.0
7	Net Blocks	SUBTRACT Openings from Gross Blocks	Ln 3 - Ln 6
8	Number of 90° Corners	See plans
8a	Height of 90° Corners in ft	See plans
9	Number of 45° Corners	See plans
9a	Height of 45° Corners in ft	See plans
10	Total Number of 90° Corner Blocks	MULTIPLY 90° Blocks per Corner by Number of Corners	Ln 8 x Ln 8a
10a	Total Number of 45° Corner Blocks	MULTIPLY 45° Blocks per Corner by Number of Corners	Ln 9 x Ln 9a
11	Number of Standard Blocks	SUBTRACT Corner Blocks From Net blocks	Ln 7- (Lns 10+10a)
12	Total Number of Top Blocks	DIVIDE Perimeter by 4.0 Minus Number of Corners	(Ln 1 ÷ 4.0) - (Lns 8 + 9)
13	Total Number of Standard Blocks	SUBTRACT Top Blocks From Standard Blocks	Ln 11 - Ln 12
14	Account for 3-4% waste 90° Corner Blocks	MULTIPLY Total 90° Corner Blocks by 1.04 **	Ln 10 x 1.04**	Total 90° Corners:
14a	Account for 3-4% waste 45° Corner Blocks	MULTIPLY Total 45° Corner Blocks by 1.04**	Ln 10a x 1.04**	Total 45° Corners:
15	Account for 3-4% waste For Top Blocks	MULTIPLY Total Top Blocks by 1.04	Ln 12 x 1.04	Total Taper/Tops:
16	Account for 3-4% waste For Standard Blocks	MULTIPLY Total Standard Blocks by 1.04	Ln 13 x 1.04	Total Standards:

* In the case where your walls have different heights, you will need to do a separate estimating sheet for each section of a different height and add all estimates to calculate your total block needed.

** Round total number of corners up to an even number (corners are packaged and shipped in pairs. You should receive your corners in bundles packed ½ lefts and ½ rights. If not, please contact your local Greenblock representative.

NOTE: All block will be rounded up to pallet counts/sizes. Check with shipping for counts.

Estimating short cut:

1. Calculate total wall sq footage (L x W x H minus square footage of windows and doors)
   
2. Divide by 4 for total block count
3. Count 90 degree corners on layout
4. Multiply number of corners times height (equals total 90 degree corners needed)
5. Repeat step 3 and 4 for 45 degree corners (equals total 45 degree corners needed)
6. Subtract corners from total block count
7. Divide total linear footage of layout by 4 to get subtotal top/taper blocks needed
8. Subtract number of corners in linear layout from top/taper blocks needed
9. Calculate total standards by subtracting from total block needed (ln 2), the 90s (ln 4), 45s (ln 5), and the top/taper blocks (ln 8)
10. Add 3-4 % to the standards for waste

Estimating Panels

1. Use the estimating sheet found at the end of this section to calculate the required quantities of each type of block required to complete your job.
2. Multiply the total from line 16 (Total Standards) by 2 to determine required panels.
3. Multiply the total from line 16 (Total Standards) by 8 to determine required webs.
   - Webs are available in 4, 6, 8, 10 or 12 inch core sizes.
4. Estimating corner block for the panel systems.
   - The 4 inch panel system utilizes corners specific to that size.
   - The 6 and 8 inch panel system utilize corners from the fixed 6 and 8 inch systems.
   - Persons using the 10 & 12 inch panel system will need to miter the corners.
5. Estimating taper/top block for the panel systems.
   - Not available in the 4”, 10” or 12”
   - The 6 and 8 inch panel systems utilize tapers/tops from the fixed 6 and 8 inch systems.

Reminder: All block will be rounded up to pallet counts/sizes. Check with shipping for counts.

Concrete Estimation

Use this basic chart for concrete calculations. Please be sure to follow the steps. Use the following for Line 6: (4” core - 81, 6” core - 54, 8” core - 40, 10” core - 32½, 12” core 27)

Ln	Objective/Outcome	Operation	Ln Ref	Calculations
1	Perimeter	ADD all sides
2	Gross Wall sq ft	MULTIPLY Perimeter by Wall Height
3	Openings sq ft	ADD each window and door sq ft to obtain total sq ft
4	Net Wall sq ft	SUBTRACT Openings sq ft from Gross Wall sq ft	Ln 2 - Ln 3
5	Corner Adjustment (Final Wall Net Sq ft)	Add corner blocks* and Subtract 1 sq ft per corner block from Net sq. ft.	Ln 4 - ?
6	Yards of Concrete Needed	DIVIDE Final Wall Net sq by ?? sq ft	Ln 5 ÷ ??

An easy way to determine how many corner blocks you have is to count how many corners there are and multiply that amount by the wall height. If you have variations in wall heights do each wall height as a separate section.

Rule of thumb concrete estimating method:

Alternate Rule of thumb:

Calculate amounts of concrete needed by using the Final Wall Net Square Footage (Line 6).

We recommend you double check your figures for concrete amount needed or have your supplier do so

	NOTE: Check with your local supplier for ⅜ aggregate and any slump/ trucking requirements.
Greenblock recommends: Minimum 2500 PSI 4.5” - 6.5” slump delivered Pea gravel ( • ⅜ aggregate) for: 4” and 6” cores
	NOTE: Larger rebar size and/or volume may require smaller aggregate for proper concrete placement and consolidation

Rebar Estimation

Rebar reinforcement within concrete walls reduces cracking and buckling under different building loads (i.e. backfill, wind, etc…) and helps manage cracking caused by temperature swings. Properly installed reinforcement around doors and windows is imperative for the buildings structural soundness.

Footing/slab dowels are often spaced every 24 inches, with a minimum of 2 horizontal rows in the footing or thickened slab. You will need to estimate the necessary rebar for required steel placement determined by codes or engineering.*

Horizontal wall rebar should be inserted as required during placement of the block in each course. Make certain you lay it with the correct overlap lengths, normally 40 times the bar diameter. As each course with horizontal rebar is laid, if possible offset it to the previous course. Continue alternating the rebar this way for the entire structure.*

Lintel steel needs to be positioned above doors and windows to support the load over these openings. Lintel rebar depends on many factors and should be calculated by an engineer or taken from PCAíS Prescription Method; or to local codes.*

Vertical rebar should be installed only after all courses and horizontal rebar have been laid. Don’t forget to put vertical rebar under the windows and within 6 inches of both sides of each opening. Check codes for vertical rebar specifications for below and above grade building. (In the rare case local codes require the vertical rebar be tied to the footing/slab dowels - use 4 ft. to 5 ft. lengths, dropping the block over the rebar.)*

If another story is to be constructed, be sure to install connecting vertical rebar. Check local codes or engineering specs for height requirements.*

All rebar placement should be calculated to local codes, ACI 318, PCAís Prescriptive Methods for ICF Residential Construction or engineers specifications.

Example Plan

Disclaimer: These estimations are given solely as an example of how to figure amounts of block, concrete and rebar for your project. Actual specifications should be provided by approved engineering tables, local codes, or the site engineer.

Example Layout (for demonstration purposes only)

From our example plan we can calculate the following:

_____Perimeter 148 linear feet
_____Exterior walls 9 feet high
_____Two 3’0” doors (21 square feet each; 42 square feet total)
_____Eight 4’x 3’ windows (12 square feet each; 96 square feet total)
_____Eight 90° corners

Rebar Estimation

Assume:

• Number 4 rebar, 20 foot sticks
• Vertical overlap between floors is 24 inches
• Horizontal overlap is 20 inches (HINT: 4 webs)
• Vertical spacing for dowels and rebar is 20 inches

Calculate Horizontal rebar

Calculate rebar needed per row in 1 course (be sure to include required overlaps) multiply that times rows or horizontal rebar needed.

_____ Perimeter 148 linear feet or 1776 linear inches
_____ Using 20 ft. sticks and 20 inches overlap = each stick will span 18’4” or 220 inches
_____ 1776 (perimeter linear inches) ÷ by 220 inches (each bars span) = 8.07 rebar required per row
_____ 9 courses
_____ +1 extra rebar bottom course
_____ +1 extra rebar top course
_____ =11 rows needed at 8.07 rebar per row
_____ = 89 - 20 foot rebar sticks needed or 1780 linear feet
_____ Doors – add one extra bar over each door
_____ To extend 24 inches either way for overlap
_____ Therefore each extra rebar will be 84 inches (36” + 24” + 24”)
_____ 2 – 3’0” doors = 2 x 84 inches = 168 inches ÷ 12 = 14 linear feet
_____ Windows – one extra bar over each window
_____ (8 – 48 inches x 36 inches) 8 x 48 inches = 384 inches
_____ add 24 inch overlap each side x8 windows = (48 inches x 8) = 384 inches
_____ 384 inches + 384 inches = 768 inches ÷ 12 = 64 ft.
_____ Footer calculate footer rebar requirements
_____ Vertical
_____ Calculate height of walls times spacing.
_____ If this story is top story, rebar should be cut 3” below top of block.
_____ If this is a connecting story rebar needs to be cut for connection to next level.

Concrete Estimation

Greenblock 6 inch Fixed Web:

_____Approximately one yard of Concrete for every 54 square feet of wall
_____Calculate amount of concrete needed by using the Net Wall Square Footage

TIP: It is recommended that you double check your figures for concrete amount needed or have your supplier do so.

Ln	Objective/Outcome	Operation	Ln Ref	Calculations
1	Perimeter	ADD all sides		20+10+14+20+14 +10+20+40=148
2	Gross Wall sq ft	MULTIPLY Perimeter by Wall Height		148X9 = 1332
3	Openings sq ft	ADD each window and door sq ft to obtain total sq ft		96+42 = 138
4	Net Wall sq ft	SUBTRACT Openings sq ft from Gross Wall sq ft	Ln 2 - Ln 3	1332-138 = 1194
5	Corner Adjustment (Final Wall Net Sq ft)	Add corner blocks* and Subtract 1 sq ft per corner block from Net sq. ft.	Ln 4 / 54	1194 / 54 = 22.11
22.11 Yards of Concrete Needed

NOTE: Check with local supplier for ⅜ aggregate and slump/trucking requirements.

Blank Estimation Worksheets

Estimating 6 inch and 8 inch Core Block (Call to estimate panel systems)

Ln	Objective/Outcome	Operation	Ln Ref	Calculations
1*	Perimeter	ADD all sides
1a*	Find Wall Height	SEE PLANS
2	Buildings wall sq ft	MULTIPLY Perimeter by Height	Ln 1 x 1a
3	Gross Blocks	DIVIDE Bldg wall sq ft by 4.0	Ln 2 ÷ 4.0
4	Square Footage of Openings	Check plans and/or Window/door schedule
5	Total Square Footage of all Openings	ADD windows & doors sq ft to obtain total sq ft	Line 4
6	Openings - Block reduction	DIVIDE Total Openings sq ft by 4.0	Ln 5 ÷ 4.0
7	Net Blocks	SUBTRACT Openings from Gross Blocks	Ln 3 - Ln 6
8	Number of 90° Corners	See plans
8a	Height of 90° Corners in ft	See plans
9	Number of 45° Corners	See plans
9a	Height of 45° Corners in ft	See plans
10	Total Number of 90° Corner Blocks	MULTIPLY 90° Blocks per Corner by Number of Corners	Ln 8 x Ln 8a
10a	Total Number of 45° Corner Blocks	MULTIPLY 45° Blocks per Corner by Number of Corners	Ln 9 x Ln 9a
11	Number of Standard Blocks	SUBTRACT Corner Blocks From Net blocks	Ln 7- (Lns 10+10a)
12	Total Number of Top Blocks	DIVIDE Perimeter by 4.0 Minus Number of Corners	(Ln 1 ÷ 4.0) - (Lns 8 + 9)
13	Total Number of Standard Blocks	SUBTRACT Top Blocks From Standard Blocks	Ln 11 - Ln 12
14	Account for 3-4% waste For 90° Corner Blocks	MULTIPLY Total 90° Corner Blocks by 1.04 **	Ln 10 x 1.04*	Total 90° Corners:
14a	Account for 3-4% waste For 45° Corner Blocks	MULTIPLY Total 45° Corner Blocks by 1.04 **	Ln 10a x 1.04*	Total 45° Corners:
15	Account for 3-4% waste For Top Blocks	MULTIPLY Total Top Blocks by 1.04	Ln 12 x 1.04	Total Taper/Tops:
16	Account for 3-4% waste For Standard Blocks	MULTIPLY Total Standard Blocks by 1.04	Ln 13 x 1.04	Total Standards:

* In the case where your walls have different heights, you will need to do a separate estimating sheet for each section of a different height and add all estimates to calculate your total block needed.

** Round total number of corners up to an even number (corners are packaged and shipped in pairs. You should receive your corners in bundles packed ½ lefts and ½ rights. If not, please contact your local Greenblock representative.

NOTE: All block will be rounded up to pallet counts/sizes. Check with shipping for counts.

Concrete Estimation for 6” core block*

Ln	Objective/Outcome	Operation	Ln Ref	Calculations
1	Perimeter ADD all sides
2	Gross Wall sq ft	MULTIPLY Perimeter by Wall Height
3	Openings sq ft	ADD each window and door sq ft to obtain total sq ft
4	Net Wall sq ft	SUBTRACT Openings sq ft from Gross Wall sq ft	Ln 2 - Ln 3
5	Yards of Concrete Needed	DIVIDE Net Wall sq. ft. by 54 sq. ft	Ln 4 / 54

Concrete Estimation for 8” core block*

Ln	Objective/Outcome	Operation	Ln Ref	Calculations
1	Perimeter	ADD all sides
2	Gross Wall sq ft	MULTIPLY Perimeter by Wall Height
3	Openings sq ft	ADD each window and door sq ft to obtain total sq ft
4	Net Wall sq ft	SUBTRACT Openings sq ft from Gross Wall sq ft	Ln 2 - Ln 3
5	Yards of Concrete Needed	DIVIDE Net Wall sq. ft. by 40 sq. ft	Ln 4 / 40

Substitute sq. ft. on line 5 above with the following to obtain:
81* for the 4 inch core system
27* for the 12 inch system

For 8” Core block
Horizontal below and above grade requirements for 8” concrete core blocks can be found by checking with national or local codes (ACI 318), engineering or PCAs Prescriptive Method for Insulating Concrete Forms in Residential Construction.Add 1% to 2% waste.

For All Other Core blocks -
Check your engineering and/or local codes. Add 1% to 2% waste.

Crew and Labor Estimating

Building with Greenblock requires:
Less manpower than most other types of construction •
Less labor than most of our ICF competitors

A good working size crew for a residential home might include:
One qualified carpenter •
Two to three laborers

Larger jobs will be finished quicker with larger crews. It helps if someone has minimal experience with concrete, but it is not mandatory.

Fixed web systems:
In general, a good building rate for a 3-4 man crew is approximately 15 forms each per hour.
_____15 forms of 6 inch = 60 square feet (15 x 4.0)
_____15 forms of 8 inch = 60 square feet (15 x 4.0)

Panel Systems:
In general, a good building rate for a 3-4 man crew is approximately 12 forms each per hour.
_____12 forms of 4 inch = 48 square feet (12 x 4.0)
_____12 forms of 6 inch = 48 square feet (12 x 4.0)
_____12 forms of 8 inch = 48 square feet (12 x 4.0)
_____12 forms of 10 inch = 48 square feet (12 x 4.0)
_____10 forms of 12 inch = 40 square feet (10 x 4.0)

Calculations include cutting and bending rebar, installing alignment systems, building and installing window and door bucks. Therefore a 3000 gross wall square foot structure may possibly require:
_____62 ½ hours labor for 6 inch panel system
_____50 hours labor for 8 inch fixed web system

Additional floors, gables, T-walls, and 45° corners may reduce overall productivity and slightly increase construction times.

TIP: Contact your local Greenblock representative for help during your first estimate, build and pour.