What R-Value Do I Need inMaryland?
Get the exact numbers required by Maryland's 2021 energy code — and find out how BGE & PEPCO rebates can help you get there for less.
Last updated: April 20, 2026 · Reviewed by Leonard Home Performance (BGE & PEPCO approved contractor, MHIC #165469)
Maryland requires R-49 for attic/ceiling insulation under the 2021 IECC for both Climate Zone 4 (most of the state) and Climate Zone 5 (Garrett County). BGE and PEPCO also require R-49 to qualify for their Home Performance with ENERGY STAR rebates.
If you've ever gotten a quote for attic insulation and wondered why your contractor keeps mentioning "R-49," this page has your answers. R-values can feel confusing — especially when older homes have wildly different levels — so we've broken down exactly what's required in Maryland, what the code actually says, and where you can save money getting there.
What Is R-Value and Why Does It Matter?
R-value is a measure of thermal resistance — how well a material slows the movement of heat. The higher the R-value, the more effective the insulation. Think of it as a thickness-independent rating: two inches of spray foam and six inches of blown-in cellulose can achieve the same R-value through very different means.
In a Maryland home, R-value directly affects how hard your HVAC system works. A poorly insulated attic is often the single biggest source of heat loss in winter and heat gain in summer. Upgrading to the right R-value — and pairing it with proper air sealing — can cut heating and cooling costs by a meaningful amount on your monthly utility bill.
Not sure what's actually in your attic right now? Our attic insulation service page explains how existing insulation is measured and what upgrade options exist.
What Climate Zone Is Maryland In?
The U.S. Department of Energy divides the country into eight climate zones, and your zone determines the minimum insulation requirements under the International Energy Conservation Code (IECC). Maryland spans two of them:
Climate Zone 4 — Most of Maryland
Covers the vast majority of the state, including Baltimore, Montgomery County, Howard County, Anne Arundel County, Prince George's County, and essentially all of Central and Southern Maryland.
Climate Zone 5 — Garrett County Only
Only Garrett County, in Maryland's far western panhandle, falls into Zone 5 due to its higher elevation and colder winters. Requirements here match or exceed Zone 4 under Maryland's current code.
The good news: Maryland has adopted a uniform attic R-value requirement of R-49 that applies across both climate zones, so there's one simple target regardless of where in the state you live.
You can verify your specific county's climate zone using the DOE IECC Climate Zone Map.
Maryland R-Value Requirements by Area of Your Home
Maryland adopted the 2021 IECC with state-specific amendments. For ceiling and wall insulation, Maryland amended the code back to 2018 IECC levels via Table R402.1.3.1 (the "Maryland Alternative R-value"), but the practical result for most homeowners is the same: R-49 for your attic is the target. Here's a breakdown by area:
| Area of Home | Climate Zone 4 (Most of MD) | Climate Zone 5 (Garrett Co.) | Notes |
|---|---|---|---|
| Attic / Ceiling | R-49 | R-49 | Maryland's most critical upgrade zone. R-38 may satisfy R-49 requirement if insulation extends fully over the wall top plate at eaves (per MD code exception). |
| Walls (above grade, wood frame) | R-13 + R-5ci | R-13 + R-10ci | Cavity insulation plus continuous exterior insulation. Existing walls are typically grandfathered unless major renovation. |
| Floors (over unconditioned space) | R-19 | R-30 | Applies to floors above garages, crawl spaces, or other unconditioned areas. |
| Crawl Space Walls | R-10 + R-6 | R-10 + R-6 | R-10 continuous + R-6 for any interior frame wall. Encapsulation often recommended alongside. |
| Basement Walls | R-10/R-2 | R-15/R-5 | Continuous/interior insulation requirements. Consult local building department for project specifics. |
| Ducts (outside conditioned space) | R-8 | R-8 | For duct diameters ≥ 3". Smaller ducts require R-6 minimum. |
Maryland's 2021 code includes a practical exception: if R-38 insulation is installed across 100% of the ceiling area and the full depth of uncompressed insulation extends over the wall top plate at the eaves, it satisfies the R-49 requirement. This can matter on older homes where rafter depth limits how much insulation you can physically fit near the eaves.
Why the Attic Is Your Biggest Priority
Of all the insulation locations listed above, the attic is where Maryland homeowners get the most bang for their buck. Heat rises, and in an under-insulated attic it escapes directly into the exterior during winter — and pours back in during Maryland's hot, humid summers.
What's Typical in Older Maryland Homes?
Many Maryland homes built before 2000 have attic insulation at R-11 to R-19 — well below today's R-49 requirement. Even homes built in the 1990s often stopped at R-30. That gap translates directly to dollars lost every month on heating and cooling.
Not sure whether your home is in that gap? Here are the telltale signs you need more attic insulation — from uneven room temperatures to ice dams to climbing utility bills.
Air Sealing: The Step You Can't Skip
R-value measures insulation's resistance to conducted heat, but air leakage — gaps around light fixtures, attic hatches, plumbing penetrations, and top plates — can defeat even high-R insulation. This is why Maryland's BGE and PEPCO rebate programs require air sealing to be completed before insulation is installed.
Learn more about what's involved in our attic air sealing service — and why skipping it leaves energy efficiency on the table.
What R-Value Do BGE and PEPCO Require for Rebates?
Both BGE (Baltimore Gas & Electric) and PEPCO (Potomac Electric Power Company) offer rebates through the Home Performance with ENERGY STAR® (HPwES) program. The target is the same as Maryland's energy code:
To qualify for insulation rebates through the HPwES program, your attic insulation project must reach R-49, and attic air sealing must be completed first. Projects that include both air sealing and insulation may qualify for the largest available rebate tier — up to $10,000 combined for qualified improvements.
How the Rebate Process Works
- Home Energy Audit — A participating contractor (like Leonard Home Performance) conducts a $100 blower door–based audit of your home. BGE and PEPCO subsidize the true cost, which is around $400.
- Improvement Recommendations — You receive a prioritized report showing which upgrades will yield the most savings, and what rebates apply.
- Installation — Work must be performed by a certified HPwES contractor. Air sealing is completed first, then insulation to R-49.
- Rebate Paid — Rebates are issued after verified completion of the work.
For a full breakdown of available rebate amounts, eligibility, and how to get started, see our BGE & PEPCO rebates page.
You can also review program details directly from the utilities:
Should You Exceed R-49?
R-49 is the code minimum and the rebate threshold — but is it necessarily the right stopping point? In most Maryland homes, going up to R-60 in the attic adds marginal cost but meaningful comfort improvement, especially in older homes with significant air leakage history.
When to Consider Going Higher
- Your home has a history of ice dams on the roofline
- You have rooms directly below the attic that feel noticeably hot in summer or cold in winter
- You're already doing a full attic insulation removal and reinstall — adding extra depth costs relatively little during that process
- Your heating system is electric (heat pumps or resistance), where every BTU saved has a higher dollar value
If your current attic insulation is contaminated, compressed, or very old, removal may be recommended before new insulation is installed. See our attic insulation removal page to understand what that process involves and when it's necessary.
What Type of Insulation Achieves R-49 in a Maryland Attic?
Blown-In Insulation (Most Common)
The most practical and cost-effective way to reach R-49 in an existing Maryland attic is blown-in insulation — either fiberglass or cellulose. These materials conform to irregular spaces and can be installed on top of existing insulation when conditions allow.
- Fiberglass blown-in: Roughly R-2.5 to R-3.5 per inch. Reaching R-49 requires approximately 14–20 inches of depth.
- Cellulose blown-in: Roughly R-3.2 to R-3.8 per inch. Reaching R-49 requires approximately 13–16 inches of depth. Made from recycled paper; a common choice for BGE/PEPCO projects.
Spray Foam (Unvented Attics)
For unvented (conditioned) attic assemblies — where insulation is applied to the roof deck rather than the attic floor — open-cell spray foam is a common choice. At roughly R-3.5 to R-3.8 per inch, reaching R-49 requires approximately 13 inches of depth. Open-cell foam also acts as an air barrier and allows the roof deck to dry inward if moisture infiltrates, which is an important consideration in Maryland's mixed-humid climate.
Trying to decide between materials? Our guide on spray foam vs. blown-in insulation breaks down cost, performance, and which is better suited for most Maryland attics.
R-Value Per Inch by Material
Different insulation materials deliver very different R-value per inch of thickness. Use this table to estimate what you currently have or what you'd need to add:
| Insulation Type | R-Value Per Inch | Inches Needed for R-49 | Common Use |
|---|---|---|---|
| Cellulose (blown-in) | R-3.2 – R-3.8 | ~13–15 inches | Most common for BGE/PEPCO upgrades; made from recycled paper |
| Fiberglass (blown-in) | R-2.2 – R-2.7 | ~18–22 inches | Widely available; good for topping off existing insulation |
| Fiberglass batts | R-2.9 – R-3.8 | ~13–17 inches | Common in older homes; prone to compression and moisture damage over time |
| Open-cell spray foam | R-3.5 – R-3.8 | ~13 inches | Unvented (conditioned) attic assemblies; applied to roof deck |
| Closed-cell spray foam | R-6.0 – R-7.0 | ~7–8 inches | Highest R-value per inch; used where space is severely limited |
| Mineral wool / rock wool (batts) | R-3.0 – R-3.3 | ~15–16 inches | Fire resistant; good moisture resistance; less common in attics |
| Rigid foam board (polyiso) | R-5.6 – R-6.5 | ~8–9 inches | Used in unvented assemblies or as continuous insulation layer |
If your attic already has some insulation (say, R-11 fiberglass batts from a 1970s build), you may be able to add blown-in on top to reach R-49 — rather than doing a full removal. Your energy audit will determine whether existing insulation is in good enough condition to keep. If it's contaminated, wet-damaged, or contains vermiculite, removal is the right first step.
Installation Quality Matters as Much as R-Value
Here's something most homeowners never hear: the R-value printed on a bag of insulation is measured under perfect lab conditions. What you actually get in your attic depends heavily on how well it was installed. The RESNET grading system — used by ENERGY STAR, BPI, and Maryland's Home Performance with ENERGY STAR program — rates every insulation job on a three-grade scale.
The difference between a Grade I and Grade III install is not cosmetic. A Grade III installation can deliver 30% or less of the rated R-value. That means R-19 insulation installed poorly performs closer to R-13 — and you'd never know it without an infrared inspection.
- Completely fills cavity side to side, top to bottom
- No visible gaps around wiring or penetrations
- Not compressed below intended depth
- Required for BGE & PEPCO rebate qualification
- Minor gaps around wiring or plumbing
- Slight rounded edges or "shoulders" at edges
- Up to 2% of surface area void or compressed
- Acceptable but not optimal
- Significant gaps around wiring, plumbing, boxes
- Batts compressed, folded, or cut too short
- More than 10% of surface area void or defective
- R-19 installed at Grade III performs like R-13
If your attic insulation was installed quickly or by a crew without quality oversight, there's a real chance it's performing at Grade II or Grade III — even if the depth looks adequate on paper. This is one of the core reasons BGE and PEPCO require a blower door test and infrared inspection as part of the audit process: you can't verify installation quality with a tape measure alone. A BPI-certified contractor installs to Grade I standards and verifies the result.
How Do You Know What You Currently Have?
The most reliable way to find out your current attic insulation level is with a professional home energy audit. However, you can get a rough sense yourself:
- Locate your attic access hatch and look at the depth of existing insulation.
- Use a ruler or tape measure. Most blown-in fiberglass is around R-2.5–3 per inch; batts are often labeled.
- If insulation is at or below 6 inches, you're almost certainly below R-19 — well short of R-49.
- If the attic floor joists (typically 2×6 or 2×8) are barely covered or fully exposed, you're at minimal or zero insulation.
A home energy audit gives you precise measurements using a blower door test and infrared thermography — so you know exactly where insulation is deficient, where air is leaking, and what the most cost-effective fixes are.
Attic Insulation Calculator
Use this tool to estimate your current R-value, then see how much more insulation you'd need to reach R-49 — Maryland's code requirement and the BGE/PEPCO rebate threshold.
Frequently Asked Questions
Maryland's 2021 IECC primarily targets new construction and major renovations. Existing homes are generally not required to upgrade insulation unless a significant structural change is underway. That said, upgrading existing attic insulation to R-49 is the standard requirement for qualifying for BGE or PEPCO rebates — and it's one of the highest-ROI improvements most Maryland homeowners can make.
No — BGE and PEPCO's Home Performance with ENERGY STAR program requires attic air sealing to be completed before insulation is installed. This is not just a rule; it's good building science. Air sealing without insulation helps some; insulation without air sealing helps less than you'd expect. Together, they're exponentially more effective.
Costs vary based on attic size, current insulation levels, and whether removal is needed. A typical attic air sealing and insulation project for a Maryland home runs $2,500–$6,000 before rebates. After BGE or PEPCO rebates (which can reach $10,000 for qualifying combined projects) and the federal 30% tax credit (up to $1,200 for insulation and air sealing), many homeowners see their out-of-pocket cost reduced significantly.
Not always. If your existing insulation is dry, uncontaminated, and in reasonable condition, new blown-in material can often be added on top to reach R-49. Removal is recommended when insulation is wet-damaged, pest-infested, moldy, or contains materials like vermiculite (which may contain asbestos). See our attic insulation removal page for more on when removal is the right first step.
Yes. PEPCO customers in Montgomery County and Prince George's County participate in the same statewide Home Performance with ENERGY STAR program as BGE customers. The R-49 attic insulation requirement applies, and the rebate structure is comparable. Leonard Home Performance works with both BGE and PEPCO customers throughout the greater Baltimore and DC metro area.