Project
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Honest articles on construction, home improvement, and project finance. Real numbers, real tradeoffs, no SEO fluff.
How Many Pavers — and the Pattern Tax Nobody Mentions
Patio area divided by paver area looks simple — but the laying pattern can swing your order by 20%. Here is the actual math, the pattern tax, and what to round up to.
Paver Base and Sand — How Much to Order
The pavers are what you see. The gravel base and sand bed under them decide whether the patio is still flat in three years. Here is how to size both — without overpaying or coming up short.
Retaining Wall Block Math (and When You Need an Engineer)
A 20-ft long, 2-ft tall retaining wall is one of the most satisfying weekend builds. The block math is simple — the math on whether you need an engineer is more important. Here is both.
How to Find Your Roof Pitch (Three Methods + What It Means)
Pitch is the single number that decides what shingles you can use, whether you need ice barrier, and how much material to actually order. Here is how to measure it three ways and what the number controls.
Roof Truss Count and Spacing — 16 vs 24 Inches On Center
Engineered trusses replaced stick framing because they drop in 30 minutes and the lumber is sized by an engineer. The math for ordering is simple — count and spacing. Here is what to know.
Roof Snow Load — How to Read Your Number and Why It Matters
Snow load is the weather number that drives roof framing in cold climates. Get it wrong by 10 psf and you are paying for lumber you do not need — or designing a collapse risk. Here is how the math works.
Floor Joist Spans — How Far Can a 2×10 Reach
How far a joist can span depends on five things — size, spacing, live load, species, grade. The IRC and AWC publish the full tables. Here is the practical version for common residential framing.
Rebar for Concrete Slabs — Spacing, Size, and How Much
Rebar in a slab does one job: hold the slab together after it cracks. The math for ordering is simple. Spacing and bar size are the decisions that drive cost.
AC Tonnage Explained — What Size AC Do I Actually Need
AC equipment is rated in tons — 1 ton = 12,000 BTU/hr. The rule of thumb is 20 BTU/ft² with sun and occupant adjustments. Oversizing is worse than slight undersizing. Here is the math.
Furnace Sizing by Climate Zone (Output vs Input BTU)
Furnace sizing is the rare HVAC call where climate matters more than house size. Atlanta vs Minneapolis on the same 2,000 ft² house can swing the size 50%. Here is the math and the AFUE conversion.
Boiler Sizing for Hydronic Heating (Radiator vs Radiant)
Hydronic boiler sizing uses the same climate-zone rule as a furnace, with adjustments for radiant floor systems and boiler AFUE class. Cast-iron lasts longer, condensing saves more fuel.
Mini-Split Sizing — BTU per Zone, Not per House
Mini-splits are sized per zone — each indoor head matches its room. Standard sizes are 9k/12k/18k/24k/36k BTU/hr. Get sizing wrong and you short-cycle or run continuously.
Water Heater Sizing — Tank Gallons or Tankless GPM
Water heater sizing is one question — can it deliver to all the things running on your busiest morning? Here is the math for tank FHR and tankless GPM, plus what changes by climate.
Topsoil — How Many Yards (or Bags) Do You Need
Topsoil math is volume — area times depth divided by 324. The decisions are quality, depth, and bulk vs bagged. Here is the practical version with what to check at the yard.
EV Charger Circuit Sizing — Wire, Breaker, and the 125% Rule
EV charging at home is a circuit-sizing problem. Get wire and breaker sized correctly per NEC and you can install Level 2 as a permitted DIY job. Here is the math.
Hardwood Flooring — Planks, Boxes, and Waste
Hardwood is sold by the box but installed plank by plank, and plank width and length drive the count. Here is the right way to size a hardwood order — and the cuts nobody plans for.
Carpet — Square Yards, Pad, and Seams
Carpet sells by the square yard from rolls 12 or 15 feet wide, and the roll width decides whether your room needs a seam. Here is the right way to size the order.
Sheet Vinyl Flooring — Linear Feet, Seams, and Waste
Sheet vinyl is the cheapest waterproof flooring you can buy — but the math is per linear foot of roll, and the roll width decides whether you need a seam. Here is how to size the order.
Fence Posts — Spacing, Concrete, and Frost Depth
A wood privacy fence is three numbers: posts, panels, concrete. Spacing is 8 ft standard; concrete depth depends on frost line. Here is the math plus the gate-post upgrade.
Deck Stain — How Much Do You Need
Deck stain coverage swings 100 ft² per gallon between smooth and weathered wood. Always count the railing. Two coats is the default. Here is the practical version.
Voltage Drop — NEC 3 / 5 Percent Rule
Voltage drop on a long run does not trip a breaker. Lights flicker, motors run hot, compressors fail in five years instead of fifteen. Here is the NEC math that prevents it.
Conduit Fill — NEC 53 / 31 / 40
Conduit fill is about heat dissipation and pull-through, not just packing wires. Here is the NEC 53/31/40 rule, the EMT and THHN tables, and why you should design at 30-35 percent.
Wire Gauge — Picking the Right AWG
Wire size is the cheap mistake that hides until inspection. Here is the NEC 310.16 75°C column, the 125% continuous-load rule, and when voltage drop forces a bump.
Circuit Breaker Sizing — NEC 240.6 in Practice
Breakers protect the wire, not the appliance. Here is NEC 240.6 standard sizes, the 80% / 125% rule, and why motors get oversized breakers on purpose.
Panel Load — NEC 220 Standard Method
"Is 200 amps enough?" is the wrong question. Run the NEC 220 Standard method with the lighting demand factor and the EV continuous bump, then you know.
Conduit Bending — Offset and 3-Bend Saddle Math
The offset, the 3-bend saddle, and the shrink that makes a 96-inch run come back exactly 96 inches. Here is the math every bender handle is printed with.
Generator Sizing — Running Watts and Surge Watts
Running watts gets you a generator that stalls when the well pump kicks in. Here is the surge math, the transfer-switch rules, and what 5 / 7.5 / 22 kW each actually backs up.
BTU Sizing — Air Conditioner For a Room
AC sizing trips up homeowners both ways. Too small never cools, too big short-cycles and leaves humidity. Here is the 20 BTU/ft² rule, the adjustments, and when you need a real Manual J.
Duct CFM — Airflow For a Heat Load
Once you know the BTU load, CFM is what carries it. Here is the sensible heat formula, the 400-per-ton rule, the right delta-T, and the static-pressure problem nobody talks about.
Manual J — Right-Sizing HVAC Equipment
The previous AC was 4 tons; the actual load is 2.5. Here is why every house in America is over-sized, and what Manual J / S / D is supposed to fix.
Refrigerant Charge — Pounds, Subcooling, and Section 608
A 3-ton AC ships pre-charged for 25 ft of line set. Run it 50 ft and you owe it a pound of refrigerant — by ounce-per-foot, not by gauge pressure.
Static Pressure — Why TESP Kills Equipment
High static pressure is the cause behind half of all HVAC warranty calls. Here is what 0.5" w.c. means, why 1-inch MERV-13 filters destroy systems, and how to measure it.
Ventilation CFM — ASHRAE 62.2 in Practice
Tight homes need mechanical ventilation. Here is the ASHRAE 62.2 whole-house formula, the kitchen and bath exhaust minimums, and HRV vs ERV.
Heat Loss — Q = U × A × ΔT for Building Envelopes
Q = U × A × ΔT is the foundation of every Manual J. Here is the math, the 99% design temp, and what to add beyond conductive loss.
Mortar & Grout — How Many Bags
Mortar holds bricks and blocks together; grout fills tile joints. They are not the same product and the bag math is different. Here is the practical version with the numbers masons use at the yard.
CMU Blocks — How Many Per Wall
CMU is sold by the count, not the square foot. The 1.125-per-ft² rule, three-bags-per-100-blocks mortar math, and when rebar is required.
Stone Veneer — Flats, Corners, Mortar
Manufactured stone veneer is sold two ways: flats by the square foot and corners by the linear foot. Get the math wrong and you either run short or eat unreturnable material. Here is the count.
Stucco — Bags Per Square Footage
Stucco bag counts depend on the system. Traditional 3-coat burns about 38 bags per 100 sq ft; 1-coat synthetic runs 8 bags. Here is the math, the lath layers, and the cure schedule.
Tuckpointing — Mortar for Repointing
Tuckpointing math is easy. Matching the mortar mix to the wall era is what saves the brick. Here is the volume math, the BIA depth rule, and the historic-mortar caveat.
Stair Stringer Layout — Rise, Run, and Cut Order
Stairs are the unforgiving part of framing. A 1/4-inch error across 14 risers becomes 3-1/2 inches of trouble at the top. Here is the math, the IRC limits, and the cut order that passes inspection.
Beam Span Basics — How Far Will a Built-Up Beam Carry?
Built-up beams from 2x stock are everywhere in residential framing. The question is always: how far can I span this? Here is the practical math, with the disclaimers that have to come with it.
Plywood Sheet Coverage — Subfloor, Walls, and Roof
Plywood is sold in big rectangles that get cut down to fit irregular framing. Forgiving on paper, brutal in practice. Here is how to estimate sheets for subfloor, walls, and roof deck without making three trips back to the lumberyard.
Rafter Length from Pitch and Run
A 6/12 rafter on a 24-ft building is not 12 feet long — it is 13.4 feet plus the overhang. Here is where the pitch factor comes from and how to lay out the cuts.
Door & Window Header Sizes — IRC Quick-Pick
Headers are the small built-up beams over framed openings. Too small and the wall sags. Too big and you waste money. Here is the simplified IRC R602.7 quick-pick for typical residential framing.
Pressure Loss in Water Pipes: Hazen-Williams Made Practical
Pressure loss is the silent killer of water systems. Everything looks fine on day one, then a fixture starves three months later. Here's the math that prevents it.
What Size Pipe for X GPM? Flow-Rate Pipe Sizing
Sometimes you don't have a fixture list — you have a flow demand. Here's the velocity-based rule pros use to size pipe by GPM for irrigation, equipment, and custom systems.
Plumbing Trap Sizes by Fixture (IPC Table 1002.1)
Get the trap size wrong and the fixture either drains slow, clogs, or vents sewer gas into the room. Here's the IPC table by fixture, plus the trap arm and vent rules that come with it.
Water Meter Sizing: When to Upsize and Why
The water meter is the single biggest restriction in most service lines. Add a tankless heater to a typical residential meter and you've eaten the entire flow capacity for the rest of the house.
Building Drain Sizing: IPC Table 710.1 Made Practical
The building drain is the main artery every branch empties into. Get the size or slope wrong and you get chronic back-ups in the lowest fixtures that keep coming back no matter how often you snake.
Wet Wall & Soil Stack Sizing for Multi-Story Homes
In multi-story houses, almost all plumbing runs vertically through one wet wall. Get the stack size wrong and you have a structural problem dressed up as a plumbing problem.
How to Size a Booster Pump for Low-Pressure Water Service
Some buildings don't get enough water pressure from the street — hilltop houses, rural service lines, top floors. The fix is a booster pump, and sizing it right means the difference between solving the problem and creating two new ones.
Expansion Tank Sizing for Closed Plumbing Systems
The blue cylinder strapped to the cold inlet of your water heater is an expansion tank, and most homeowners ignore it until it fails. Here's why closed systems need them and how to size and install one right.
How Much Paint Do I Need? Real Coverage Math
The reason you usually buy too much paint is that gallons don't cover what the label says. Real coverage is 200–325 ft² per gallon, not 350. Here's the actual math.
What Size Water Supply Line for a House? Plumbing Pipe Sizing Guide
Pick the wrong supply line and your shower drops to a trickle when someone flushes — or you waste money on oversized copper. Here's the IPC method pros use to find the right size.
How Much Tile for a Bathroom? Floor and Wall Math
Tile is where almost everyone underbuys — the 10% waste rule from drywall is too low, and box quantities don't map to your room size. Here's how to estimate without coming up short.
How Much Concrete Do I Need? Cubic Yards, Bags, and Real-World Examples
The honest answer: it depends on what you're pouring, how thick, and whether the ground is level. But you can get a usable number in 30 seconds. Here's how the math works, plus the rules of thumb pros use.
Drywall Estimating: How to Figure Sheets for Any Room
The math has a couple of gotchas that turn an easy job into a second trip to Home Depot. This guide walks through the formula, when to use 4×8 vs 4×12, and how to handle ceilings, openings, and waste.
How Many Shingles for My Roof? A Pitched-Roof Guide
Roofing math intimidates people because of one term: pitch. Once you know how pitch affects square footage, the rest is simple. Here's how to figure bundles, plus the cost numbers most online calculators skip.
Mulch by the Yard or by the Bag? When Each Wins
Bagged mulch is convenient. Bulk by the yard is dramatically cheaper. The crossover where bulk wins isn't obvious — it depends on volume, hauling, and depth. Here's the breakeven math.
Mortgage P&I vs PITI: What Your Real Monthly Cost Will Be
The number on a mortgage calculator is almost never your real monthly housing cost. P&I (principal and interest) is what calculators show. PITI (with taxes and insurance) is what shows up in your bank account.