License #565275

Customer Reviews

Customer Reviews

At Cornerstone Windows & Patio Doors, we combine the best window and door products with superior service.

With more than 3 decades of construction expertise, we’ve developed an installation system that eliminates damage to stucco and drywall. Our expert, in-house installers go to great lengths to protect your floors and furniture as they work. Most projects are completed in a single day.

Customers often compliment our installers. We thrive on these wonderful business relationships while serving residents throughout the South Bay and West Los Angeles areas.

Katie RomeroKatie Romero
18:38 23 Dec 22
Wow! First of all Tony and Tina ( owners) are wonderful. Tina could not have been more friendly and personable and Tony was awesome and very patient, giving me multiple bids due to me changing my mind on the types of windows I wanted.Tony, Antonio, Mike and Steven showed up on time and spent the whole day replacing all the windows in my house plus a sliding door. Antonio kept me up to date with their progress and consulted me with things he thought I should know. He showed me how to open and... close the long, slider windows from the middle to ensure their longevity and proper alignment and how to remove and replace the screens. They even swept up the leaves in my patio along with the glass!Overall, this a been a wonderful experience, great customer service, great products, wonderful staff!read more
Amy HoppesAmy Hoppes
22:23 20 Nov 20
Cornerstone Windows & Doors (Tony Szik, the owner) is very professional. I really appreciate how courteous and efficient he was with the repair of a window. He is licensed, was on time, very efficient and did a great job! We’ve been hiring Cornerstone to do work on our house over the last ten years and we couldn’t be happier! They are trustworthy!
Rick KamrathRick Kamrath
19:50 22 Aug 19
Since they only just finished the job, I cannot comment on the quality of windows we purchased from Cornerstone, OR any warranty-related issues. What I CAN say is that their staff is professional and a pleasure to work with. The installation was on time and ALL their installers as polite as they were professional. Because we were so happy with dealing with Cornerstone, we cannot comment on "value" because we didn't bother getting prices from anyone else.
Craig ChapmanCraig Chapman
22:23 08 Apr 19
Tony and his crew did an awesome job on our home! Had all 13 windows and 3 sliders replaced and couldn’t be happier. I would definitely recommend them for any job big or small!!!
Carlyn GoreCarlyn Gore
18:37 31 Jan 19
Very professional company, and workmanship outstanding. Would recommend to my friends for repairs and or replacement of windows and doors.

Customer Messages

“I just wanted to thank you for the great job your company did for our window installation. They look so great and the workers were all so professional, punctual, and friendly. Much appreciated! Thank you!”  – Andy O.

“Hi Tony, Just wanted to let you know the Simonton windows you put in my place a couple years back that are tall ocean facing sliders survived last night’s wind storm, and kept me nice and cozy!

These windows have been solid on hot days,  windy days, rainy days etc. Thank you so much for installing this quality product for me. I hope everything is going well in your business, and here’s to a great holiday season ahead for you” – Linda C, November 2022


Angie’s List

“Cornerstone made it simple and easy to get all of our windows replaced. They had a full crew, arrived on time, spread protective covers over everything, and handled the entire window replacement process (including sliders and screens) in a quick and professional manner. We had investigated several other firms and took the recommendations of our complex’s maintenance manager and went with Cornerstone. Based on results, it was one of the best recommendations we have ever received for any kind of home maintenance, upgrade and repair work.”  -Angieslist.com, Mike R. of Rancho Palos Verdes

“From our initial visit in the showroom to the consultation and measuring in our home and then the installation, the products, staff, professionalism and the experience was outstanding.” – Angieslist.com,  Ed B.  of Rancho Palos Verdes

“Excellent!!! extremely pleased with installation of 17 windows. The crew were friendly and very clean. I will be sure to have referals, and my business again” –  Angieslist.com, Diamond S. of Los Angeles.

“I am writing this review because I broke the handle on my sliding door today and went to their shop to inquire about a replacement. They immediately brought me the replacement handle and off I went. No hassles. Cornerstone was awesome when they did the install several years ago. Punctual. Professional. No surprises. My two experiences with Cornerstone have been great and I would recommend them to anyone looking to replace windows or doors. ” -Angieslist.com, Sandra M. of Redondo Beach


“We love our new windows!!! Tony was awesome and answered all our questions. The installers did a fantastic job! Everyone we dealt with was very professional and courteous. They were also very reasonably priced. We would definitely recommend them and will use them again. Thanks guys! :)” – Yelp review, Jaime E. of Lakewood.

“Good price, good quality and professional installation with a great warranty. They were always on time for appointments. I would definitely do business with them again and refer them to family and friends or anyone looking for replacement windows.” – Yelp review from Chris M. of Palos Verdes.

“The windows themselves (Milgard) are perfect! I couldn’t have wished for a better design. They are a very close replica of what we had originally. I am really happy with them, really happy with Cornerstone & I would highly recommend them.” – Yelp review from Rebecca P. of Hermosa Beach.


“A pure pleasure to work with this company. Cornerstone should be very proud of their employees. The fellas that installed my windows were timely, courteous and well mannered. I would recommend them in a heartbeat.” – Yahoo review, Annie.

“Cornerstone Windows met all if its deadlines as promised, performed quality workmanship and had the best price in town. I would highly recommend Cornerstone for any remodeling or construction job relative to windows and doors. From the owner to the sales & office staff to their excellent installation team, I couldn’t have asked for more excellent service.” – Yahoo review, satisfied customer.

We Exceed Expectations

Cornerstone is dedicated to surpassing your expectations for window and door installations.

Contact our window replacement experts now at 310-325-4700 for a free in-home estimate.

Tony Szik's Cornerstone Doors & Windows, Inc., Door Installation, Torrance, CA

Cornerstone Windows is A+ rated from the Better Business Bureau since 2002